ENGR00223056 Fix HDMI build warning

ENGR00223056 Fix HDMI build warning

Fix HDMI build warning.
drivers/video/mxc_hdmi.c: In function 'mxc_hdmi_set_mode':
drivers/video/mxc_hdmi.c:1659: warning: assignment discards
 qualifiers from pointer target type
drivers/video/mxc_hdmi.c: At top level:
driver/video/mxc_hdmi.c:1398: warning: 'mxc_hdmi_enable_pins'
 defined but not used

Remove unused function mxc_hdmi_enable_pins() and mxc_hdmi_disable_pins()
from code. Fix defined but unused function build warning.
Added pointer conversion from const poniter to non-const pointer.

Signed-off-by: Sandor Yu <R01008@freescale.com>