platform: x86: MLX_PLATFORM: select REGMAP instead of depending on it

REGMAP is a hidden (not user visible) symbol. Users cannot set it
directly thru "make *config", so drivers should select it instead of
depending on it if they need it.

Consistently using "select" or "depends on" can also help reduce
Kconfig circular dependency issues.

Therefore, change the use of "depends on REGMAP" to "select REGMAP".

Fixes: ef0f6226 ("platform/x86: mlx-platform: Add physical bus number auto detection")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Vadim Pasternak <vadimp@mellanox.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mark Gross <markgross@kernel.org>
Cc: platform-driver-x86@vger.kernel.org
Link: https://lore.kernel.org/r/20230226053953.4681-7-rdunlap@infradead.org


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>