s390: Replace __ASSEMBLY__ with __ASSEMBLER__ in non-uapi headers

s390: Replace __ASSEMBLY__ with __ASSEMBLER__ in non-uapi headers

While the GCC and Clang compilers already define __ASSEMBLER__
automatically when compiling assembler code, __ASSEMBLY__ is a
macro that only gets defined by the Makefiles in the kernel.
This is bad since macros starting with two underscores are names
that are reserved by the C language. It can also be very confusing
for the developers when switching between userspace and kernelspace
coding, or when dealing with uapi headers that rather should use
__ASSEMBLER__  instead. So let's now standardize on the __ASSEMBLER__
macro that is provided by the compilers.

This is a completely mechanical patch (done with a simple "sed -i"
statement), with some manual fixups done later while rebasing the
patch.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20250611140046.137739-3-thuth@redhat.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>