MAINTAINERS: match mxc in file names by IMX / MXC entry

MAINTAINERS: match mxc in file names by IMX / MXC entry

There is a number of i.MX-related drivers that have mxc in their name,
but are not matched by the i.MX MAINTAINERS entry, most notably the GPIO
driver, which is still being used on current SoCs.

Looking at current files containing mxc in their name, all of them are
related to i.MX, except for:

  drivers/iio/accel/mxc4005.c
  drivers/iio/accel/mxc6255.c
  tools/testing/selftests/powerpc/tm/tm-vmxcopy.c

Therefore adapt the regex to match all mxc files, except those above.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>