nds32: Remove phys_initrd_start and phys_initrd_size

This will conflict with a subsequent change making phys_initrd_start and
phys_initrd_size global variables. nds32 does not make use of those nor
provides a suitable declarations so just get rid of them.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Rob Herring <robh@kernel.org>

arch/nds32/mm/init.c

@@ -21,8 +21,6 @@
 DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
 DEFINE_SPINLOCK(anon_alias_lock);
 extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
-extern unsigned long phys_initrd_start;
-extern unsigned long phys_initrd_size;
 
 /*
  * empty_zero_page is a special page that is used for