Machin dependent serial port patches

[J.C. Wren]

	One of the things I noticed in the port of 2.5.69 to the 386EX embedded 
system is that serial.h appears to not be a mach-xxx positionable file.  The 
386EX board uses standard 8250 type serial ports, but at 3.6864Mhz instad of 
1.8432Mhz.  There appears to be no way to build a patch set without modifying 
include/i386/serial.h.  Would this not be better places in mach-defaults?  
I'm trying very hard to modify as few files as possible when building these 
patch sets.

	--John