powerpc/book3e: Fix build error

arch/powerpc/mm/nohash/fsl_book3e.c: In function ‘relocate_init’:
arch/powerpc/mm/nohash/fsl_book3e.c:348:2: error: implicit declaration of function ‘early_get_first_memblock_info’
  early_get_first_memblock_info(__va(dt_ptr), &size);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Add missing include file linux/of_fdt.h to fix this.

Fixes: 86c38fec ("powerpc: Remove asm/prom.h from all files that don't need it")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220517094830.27560-1-yuehaibing@huawei.com