mfd: arizona: Remove duplicate select of MFD_CORE

MFD_ARIZONA_I2C and MFD_ARIZONA_SPI both select MFD_ARIZONA and all
three of those select MFD_CORE, this makes the selects of MFD_CORE in
MFD_ARIZONA_I2C and MFD_ARIZONA_SPI redundant, so we remove them.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>