iio: adc: Add support to read parallel charger current channel

Add support to read ADC channel 0xA5 for parallel charger
current.

Some PMICs (PMI632) the max supported current is 5A, hence
define a new config data and compatible string for it.

Change-Id: I973dfdf81ee955d322da7e2c328d8b1472d33013
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>