phy: ralink: Kconfig: convert mt7621-pci-phy into 'bool'

Make dependent on PCI_MT7621 configuration option and mark
this pci phy configuration as bool which has more sense.
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210508070930.5290-6-sergio.paracuellos@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/ralink/Kconfig

@@ -3,8 +3,8 @@
 # PHY drivers for Ralink platforms.
 #
 config PHY_MT7621_PCI
-	tristate "MediaTek MT7621 PCI PHY Driver"
-	depends on (RALINK && OF) || COMPILE_TEST
+	bool "MediaTek MT7621 PCI PHY Driver"
+	depends on (RALINK && OF && PCI_MT7621) || COMPILE_TEST
 	select GENERIC_PHY
 	select REGMAP_MMIO
 	help