NFC: Add support for LDO voting

Vote for LDO regulator during probe() if LDO related
properties are present in the device tree otherwise
we will avoid LDO configuration as it's optional.

Configure VEN gpio low and unvote for LDO during driver unloading.

Change-Id: I36ecdc5cef5afb6ddb0ef6ea4db6e745e567ab7b
Signed-off-by: Gaurav Singhal <gsinghal@codeaurora.org>