mfd: axp20x: Use DEFINE_RES_IRQ to declare resources for mfd_cells

Previously we were open coding the interrupts for the various mfd
cells. This made the code somewhat long due to pretty-formatting.

This patch convert those into one-line declarations with DEFINE_RES_IRQ,
making the code shorter and easier to read.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>