powerpc/kexec_file: fix implicit decl error

kexec (PPC64) code calls memory_hotplug_max(). Add the header
declaration for it from <asm/mmzone.h>. Using <linux/mmzone.h> does not
work since the #include for <asm/mmzone.h> depends on CONFIG_NUMA=y,
which is not always set.

Fixes this build error/warning:

  arch/powerpc/kexec/file_load_64.c: In function 'kexec_extra_fdt_size_ppc64':
  arch/powerpc/kexec/file_load_64.c:993:33: error: implicit declaration of function 'memory_hotplug_max'
  993 |                 usm_entries = ((memory_hotplug_max() / drmem_lmb_size()) +
      |                                 ^~~~~~~~~~~~~~~~~~

Fixes: fc546fa ("powerpc/kexec_file: Count hot-pluggable memory in FDT estimate")
Signed-off-by: Randy Dunlap <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: rddunlap

arch/powerpc/kexec/file_load_64.c

@@ -26,6 +26,7 @@
 #include <asm/firmware.h>
 #include <asm/kexec_ranges.h>
 #include <asm/crashdump-ppc64.h>
+#include <asm/mmzone.h>
 #include <asm/prom.h>
 
 struct umem_info {