imx6dq: Fix chip version issue for rev1.3

According to iMX6DQ RM, the minor field (low 8 bits) in DIGPROG is not
aligned on silicon revision 1.3. So update get_cpu_rev to correct the
revision.

0x00630002 Silicon revision 1.2
0x00630005 Silicon revision 1.3
0x00630006 Silicon revision 1.6

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>