powerpc: Mark memory_limit as initdata

The `memory_limit` variable should only be used during boot, enforce
that by marking it initdata.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240422115231.1769984-1-mpe@ellerman.id.au

arch/powerpc/mm/mem.c

@@ -30,7 +30,7 @@
 
 #include <mm/mmu_decl.h>
 
-unsigned long long memory_limit;
+unsigned long long memory_limit __initdata;
 
 unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
 EXPORT_SYMBOL(empty_zero_page);