Add mpzqlp2ctl entry for mx6_mmdc_calibration.
MMDC_MPZQLP2CTL register is for init tZQINIT, tZQCL, tZQCS for LPDDR2 chips.
Signed-off-by: NPeng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Tim Harvey <tharvey@gateworks.com>