ARM: 8022/1: ftrace: work with CONFIG_DEBUG_SET_MODULE_RONX

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,
84e1c6bb ("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>