powerpc: 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 standardize now on the __ASSEMBLER__
macro that is provided by the compilers.

This is almost a completely mechanical patch (done with a simple
"sed -i" statement), apart from tweaking two comments manually in
arch/powerpc/include/asm/bug.h and arch/powerpc/include/asm/kasan.h
(which did not have proper underscores at the end) and fixing a
checkpatch error about spaces in arch/powerpc/include/asm/spu_csa.h.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250801082007.32904-3-thuth@redhat.com

arch/powerpc/include/asm/nohash/64/pgtable.h

@@ -77,7 +77,7 @@
 
 #define H_PAGE_4K_PFN 0
 
-#ifndef __ASSEMBLY__
+#ifndef __ASSEMBLER__
 /* pte_clear moved to later in this file */
 
 #define PMD_BAD_BITS		(PTE_TABLE_SIZE-1)
@@ -209,6 +209,6 @@ void __patch_exception(int exc, unsigned long addr);
 	__patch_exception((exc), (unsigned long)&name); \
 } while (0)
 
-#endif /* __ASSEMBLY__ */
+#endif /* __ASSEMBLER__ */
 
 #endif /* _ASM_POWERPC_NOHASH_64_PGTABLE_H */