ARM: imx: correct gpu2d_axi and gpu3d_axi clock setting

On i.MX6Q, gpu2d_axi and gpu3d_axi are either from AXI or
AHB clock, but on i.MX6DL, gpu2d_axi and gpu3d_axi are
from mmdc_ch0_axi_podf, and they can NOT be gated by mmdc_ch0_axi
's clock gate, the mux option register field(CCM_CBCMR)
is marked as "Reserved" now on i.MX6DL RM, so correct these
two clks setting.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>