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>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
diff --git a/configs/linkit-smart-7688-ram_defconfig b/configs/linkit-smart-7688-ram_defconfig
index 6e9aa7a..c2502b2 100644
--- a/configs/linkit-smart-7688-ram_defconfig
+++ b/configs/linkit-smart-7688-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_BOARD_LINKIT_SMART_7688=y
 # CONFIG_MIPS_BOOT_ENV_LEGACY is not set
 CONFIG_MIPS_BOOT_FDT=y