headers: Fix PENUM_PAGE_FILE_CALLBACK declaration for x86

This fixes invalid conversion error in x86 while using EnumPageFiles API.
Instead of using __stdcall keyword directly, this patch adds CALLBACK macro
for ARM cases also.

Signed-off-by: Biswapriyo Nath <nathbappai@gmail.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>