mfd: sec-core: Dump PMIC revision to find out the HW

There are different revisions of the same chipset. For example S2MPS13 has
more than 2 revisions. They differ slightly in regulator constraints.
Print the revision number to easily find which PMIC is used on the board.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>