mips: rename mach-mt7620 to mach-mtmips

Currently mach-mt7620 contains only support for mt7628. To avoid confusion,
rename mach-mt7620 to mach-mtmips, which means MediaTek MIPS platforms.
MT7620 and MT7628 should be distinguished by SOC_MT7620 and SOC_MT7628
because they do not share the same lowlevel codes.

Dependencies of four drivers are changed to SOC_MT7628 as these drivers
are only used by MT7628.

Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/gardena-smart-gateway-mt7688-ram_defconfig b/configs/gardena-smart-gateway-mt7688-ram_defconfig
index 7c8ae0f..e099506 100644
--- a/configs/gardena-smart-gateway-mt7688-ram_defconfig
+++ b/configs/gardena-smart-gateway-mt7688-ram_defconfig
@@ -1,7 +1,7 @@
 CONFIG_MIPS=y
 CONFIG_SYS_TEXT_BASE=0x80010000
 CONFIG_NR_DRAM_BANKS=1
-CONFIG_ARCH_MT7620=y
+CONFIG_ARCH_MTMIPS=y
 # CONFIG_MIPS_BOOT_ENV_LEGACY is not set
 CONFIG_MIPS_BOOT_FDT=y
 CONFIG_ENV_VARS_UBOOT_CONFIG=y