x86/boot: Add kstrtoul() from lib/

Add kstrtoul() to ../boot/ to be used by facilities there too.

 [
   bp: Massage, make _kstrtoul() static. Prepend function names with
   "boot_". This is a temporary workaround for build errors like:

   ld: arch/x86/boot/compressed/acpi.o: in function `count_immovable_mem_regions':
   acpi.c:(.text+0x463): undefined reference to `_kstrtoul'
   make[2]: *** [arch/x86/boot/compressed/Makefile:117: arch/x86/boot/compressed/vmlinux] Error 1

   due to the namespace clash between x86/boot/ and kernel proper.
   Future reorg will get rid of the linux/linux/ namespace as much as
   possible so that x86/boot/ can be independent from kernel proper. ]

Signed-off-by: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/1587645588-7130-2-git-send-email-vamshi.k.sthambamkadi@gmail.com

arch/x86/boot/string.h

@@ -30,4 +30,5 @@ extern unsigned long long simple_strtoull(const char *cp, char **endp,
 					  unsigned int base);
 
 int kstrtoull(const char *s, unsigned int base, unsigned long long *res);
+int boot_kstrtoul(const char *s, unsigned int base, unsigned long *res);
 #endif /* BOOT_STRING_H */