powerpc/fsl: Modernise mt/mfpmr

With the addition of the machine directives, these are no longer simple
1-2 liner macros. So modernise them to be static inlines and use named
asm parameters.

Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240229122521.762431-4-mpe@ellerman.id.au