powerpc: Replace __ASSEMBLY__ with __ASSEMBLER__ in uapi headers

powerpc: Replace __ASSEMBLY__ with __ASSEMBLER__ in uapi headers

__ASSEMBLY__ is only defined by the Makefile of the kernel, so
this is not really useful for uapi headers (unless the userspace
Makefile defines it, too). Let's switch to __ASSEMBLER__ which
gets set automatically by the compiler when compiling assembler
code.

This is a completely mechanical patch (done with a simple "sed -i"
statement).

Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250801082007.32904-2-thuth@redhat.com