ARM: constify machine_desc structure uses

struct machine_desc records are defined everywhere as a 'const'
structure, but unfortuantely it loses its const-ness through the use of
linker magic - the symbols which surround the section are not declared
const so it becomes possible not to use 'const' for pointers to these
const structures.

Let's fix this oversight - all pointers to these structures should be
marked const too.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: ff69a4c855066592f9e293cff8f54813614dd544
[joonwoop@codeaurora.org: fixed trivial merge conflict. constify some
 more code to avoid warning.]
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>