x86 BIOS interface for RTC on SGI UV

Real-time code needs to know the number of cycles per second
on SGI UV.  The information is provided via a run time BIOS
call.  This patch provides the linux side of that interface.
This is the first of several run time BIOS calls to be defined
in uv/bios.h and bios_uv.c.

Note that BIOS_CALL() is just a stub for now.  The bios
side is being worked on.

Signed-off-by: Russ Anderson <rja@sgi.com>
Cc: Jack Steiner <steiner@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>