pmic:i2c: Add I2C sensor byte order (big/little) to PMIC framework

Since the pmic_reg_read is the u32 value, the order in which bytes
are placed to form u32 value is important.

Support for big and little sensor endianess is added.

Moreover calls to [leXX|beXX]_to_cpu have been added to support
little and big endian SoCs.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>