x86: change write msr functions interface

This patche changes the native_write_msr() and friends interface
to explicitly take 2 32-bit registers instead of a 64-bit value.
The change will ease the merge with 64-bit code. As the 64-bit
value will be passed as two registers anyway in i386,
the PVOP_CALL interface has to account for that and use low/high parameters
It would force the x86_64 version to be different.

The change does not make i386 generated code less efficient. As said above,
it would get the values from two registers anyway.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>