[ARM] Setting read-only section MMU entries as read only.

The linker script sections have been reorganized and split to set
different places for read-only and read-write sections, and the
MMU L2 entries are now set as priviledged read-write access or
priviledged read-only access.

The ".init" section is divided into two parts ".init.text" for code
and ".init.data" for data. Among this ".init.text" will be read-only
and ".init.data" will be read-write.

Uninitialized data have been set into the '.bss' sections.

Signed-off-by: Jimmy Durand Wesolowski <jimmy.durand-wesolowski@openwide.fr>