The LDO line (1V8) used by MAX30101 can be enabled using a regulator
device instead of custom code in the board pinmux.c. The same applies
for the 3V3 line used by multiple sensors.
NOTE: also enabled gpioa, required by LDO_EN. Spotted thanks to
build-time issue (current code did not work...).
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>