spi: add support for MediaTek MT7621 SoC

This patch makes mt7621_spi driver available for MediaTek MT7621 SoC

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 766d563..75b7945 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -254,7 +254,7 @@
 
 config MT7621_SPI
 	bool "MediaTek MT7621 SPI driver"
-	depends on SOC_MT7628
+	depends on SOC_MT7621 || SOC_MT7628
 	help
 	  Enable the MT7621 SPI driver. This driver can be used to access
 	  the SPI NOR flash on platforms embedding this Ralink / MediaTek