ARM: imx: add i.MX7ULP SoC revision support

i.MX7ULP SoC's revision info is inside the SIM module,
bit[31:28] of JTAG_ID register defines revision as below
from B0:

0001        B0
0010        B1

This patch adds SoC revision support for i.MX7ULP, test
result as below:

root@imx7ulp-evk ~$ cat /sys/devices/soc0/revision
2.1

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>