MLK-14938-22 mxc_gpio: Change to get value from DR register

MLK-14938-22 mxc_gpio: Change to get value from DR register

Currently the driver gets value from PSR register, but this register
is only for input mode. For output mode, it always return 0 not the
value we set for output.

This patch changes to use DR register, which returns the DR value for
output mode, and PSR value for input mode.

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit 4afc3f90943c6b117f79b66d2cd04e64f437b0c2)
(cherry picked from commit 8cca3efba0d508b2c267f8a32b302970dd05244d)