powerpc/rtas: remove lock and args fields from global rtas struct

Only code internal to the RTAS subsystem needs access to the central
lock and parameter block. Remove these from the globally visible
'rtas' struct and make them file-static in rtas.c.

Some changed lines in rtas_call() lack appropriate spacing around
operators and cause checkpatch errors; fix these as well.

Suggested-by: Laurent Dufour <ldufour@linux.ibm.com>
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Laurent Dufour <laurent.dufour@fr.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230124140448.45938-4-nathanl@linux.ibm.com