ARM: mx50: Add support to get the silicon revision

For MX50, the HW_ADADIG_DIGPROG register in the ANATOP module will
have the correct silicon revision:

Major       Minor   Description
0x50        0x0     TO1.0
0x50        0x1     TO1.1

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>