mfd: max77693: Add TORCH_IOUT_MASK macro

Add a macro for obtaining the mask of ITORCH register bit fields
related either to FLED1 or FLED2 current output. The expected
arguments are TORCH_IOUT1_SHIFT or TORCH_IOUT2_SHIFT.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>