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: ef0f622 ("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>

drivers/platform/x86/Kconfig

@@ -955,7 +955,8 @@ config SERIAL_MULTI_INSTANTIATE
 
 config MLX_PLATFORM
 	tristate "Mellanox Technologies platform support"
-	depends on I2C && REGMAP
+	depends on I2C
+	select REGMAP
 	help
 	  This option enables system support for the Mellanox Technologies
 	  platform. The Mellanox systems provide data center networking