leds: Make LEDS_TI_LMU_COMMON invisible

Currently, LEDS_LM3697 and LEDS_LM36274 depend on LEDS_TI_LMU_COMMON,
which contains the common code to support TI LMU devices.  This means
the user is asked about the common code first, followed by the
individual drivers, if their dependencies are met.

Simplify this, and reduce the number of questions by making
LEDS_TI_LMU_COMMON invisible, and letting it be selected when needed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Pavel Machek <pavel@ucw.cz>
Link: https://lore.kernel.org/r/91f6efaa48c36320e58b6a312025ae9b39ee206b.1683644796.git.geert+renesas@glider.be


Signed-off-by: Lee Jones <lee@kernel.org>