nvmem: add i.MX7 support to snvs-lpgpr

The i.MX7 family has similar SNVS hardware so make the snvs-lpgpr
support it along with the i.MX6 family. The register interface is the
same except for the number and offset of the general purpose registers.

Signed-off-by: Andrey Yurovsky <yurovsky@gmail.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>