arm: provision page alloc debug support

Equip arm to support ARCH_SUPPORTS_DEBUG_PAGEALLOC and
enable it by default.

Having this support means all pages freed at buddy level
would be marked as read-only and would help catch any
scribbling over free page area. Allocated pages mapping
attributes is restored to read/write.

ARCH_SUPPORTS_DEBUG_PAGEALLOC needs FORCE_PAGES which
ensures all kernel mapping are populated with page
granularity and it would ensure page level accesses  can
be rightly configured.

Change-Id: I9b23d1fb0b9594cc148b082c104da9a773c26057
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>