MAINTAINERS: Move Milo Kim to credits

Milo Kim's email in TI bounces with permanent error (550: Invalid
recipient).  Last email from him on LKML was in 2017.  Move Milo Kim to
credits and remove the separate driver entries for:
 - TI LP855x backlight driver,
 - TI LP8727 charger driver,
 - TI LP8788 MFD (ADC, LEDs, charger and regulator) drivers.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>