Add a KSPP recommendations config for arm

The arm section of the KSPP Recommended_Settings wiki page contains the
following lines:

 # If building an old out-of-tree Qualcomm kernel, this is similar to
 # CONFIG_STRICT_KERNEL_RWX.
 CONFIG_STRICT_MEMORY_RWX=y

Since this option only applies to an old out-of-tree Qualcomm kernel,
it is not included in the config file.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>