m32r: make PAGE_SIZE available to assembly.

page.h includes ifndef __ASSEMBLY__ guards, but PAGE_SIZE is defined
using "1UL", which the assembler does not support. Use the _AC macro
from const.h to make it available to assembly (and linker scripts).

Signed-off-by: Tim Abbott <tabbott@ksplice.com>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>