bootparam.7: Remove crufty "Serial port drivers" options

[Part of a general change to remove cruft from this page.]
Much of the detail on device-driver specifics in this page dates
from the 20th century. (The last major update to this page was in
man-pages-1.14!) It's hugely out of date now (many of these
devices disappeared from the kernel years ago.) Arguably, this
kind of detail should never have been placed in a man page to
begin with, since devices come and go. Remove such text, and
where appropriate and possible add pointers to files in the
kernel Documentation/ directory.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/bootparam.7

@@ -799,87 +799,6 @@ As you can see, it gets pretty messy, and you are better off to compile
 in your own personal values as recommended.
 Using a boot argument of
 \&'sound=0' will disable the sound driver entirely.
-.SS Serial port drivers
-.TP
-.B "The RISCom/8 Multiport Serial Driver ('riscom8=')"
-Syntax:
-
-.in +4n
-.nf
-riscom=iobase1[,iobase2[,iobase3[,iobase4]]]
-.fi
-.in
-.IP
-More details can be found in the kernel source file
-.IR Documentation/riscom8.txt .
-.TP
-.B "The DigiBoard Driver ('digi=')"
-If this option is used, it should have precisely six parameters.
-Syntax:
-
-.in +4n
-.nf
-digi=status,type,altpin,numports,iobase,membase
-.fi
-.in
-.IP
-The parameters maybe given as integers, or as strings.
-If strings are used, then iobase and membase should be given
-in hexadecimal.
-The integer arguments (fewer may be given) are in order:
-status (Enable(1) or Disable(0) this card),
-type (PC/Xi(0), PC/Xe(1), PC/Xeve(2), PC/Xem(3)),
-altpin (Enable(1) or Disable(0) alternate pin arrangement),
-numports (number of ports on this card),
-iobase (I/O Port where card is configured (in HEX)),
-membase (base of memory window (in HEX)).
-Thus, the following two boot prompt arguments are equivalent:
-
-.in +4n
-.nf
-digi=E,PC/Xi,D,16,200,D0000
-digi=1,0,0,16,0x200,851968
-.fi
-.in
-.IP
-More details can be found in the kernel source file
-.IR Documentation/digiboard.txt .
-.TP
-.B "The Baycom Serial/Parallel Radio Modem"
-Syntax:
-
-.in +4n
-.nf
-baycom=iobase,irq,modem
-.fi
-.in
-.IP
-There are precisely 3 parameters; for several cards, give
-several 'baycom=' commands.
-The modem parameter is a string
-that can take one of the values ser12, ser12*, par96, par96*.
-Here the * denotes that software DCD is to be used, and
-ser12/par96 chooses between the supported modem types.
-For more details, see the file
-.I Documentation/networking/baycom.txt
-(or
-.I drivers/net/README.baycom
-for older kernels) in the Linux kernel source.
-.TP
-.B "Soundcard radio modem driver"
-Syntax:
-
-.in +4n
-.nf
-soundmodem=iobase,irq,dma[,dma2[,serio[,pario]]],0,mode
-.fi
-.in
-.IP
-All parameters except the last are integers;
-the dummy 0 is required because of a bug in the setup code.
-The mode parameter is a string with syntax hw:modem,
-where hw is one of sbc, wss, or wssfdx, and modem is one of
-afsk1200 or fsk9600.
 .SS The line printer driver
 .TP
 .B "'lp='"