Make ftrace work with CONFIG_DEBUG_SET_MODULE_RONX by making module text
writable around the place where ftrace does its work, like it is done on
x86 in the patch which introduced CONFIG_DEBUG_SET_MODULE_RONX, 84e1c6bb38eb ("x86: Add RO/NX protection for loadable kernel modules").
Tested-by: Mitchel Humpherys <mitchelh@codeaurora.org> Signed-off-by: Rabin Vincent <rabin@rab.in> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>