mtd: Make CONFIG_MTD be the gate symbol for the menu

The help for CONFIG_MTD explains that it needs to be enabled for various
things like NAND, etc to be available. It however then doesn't enforce
this dependency and so if you have none of these systems present you
still need to disable a number of options. Fix this by making places
that select/imply one type of flash, but did not do the same, also do
this for "MTD". Make boards which hadn't been enabling MTD already but
need it now, do so. In a few places, disable CONFIG_CMD_MTDPARTS as it
wasn't previously enabled but was now being implied.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/microchip/mpfs_icicle/Kconfig b/board/microchip/mpfs_icicle/Kconfig
index ce510e2..4309f75 100644
--- a/board/microchip/mpfs_icicle/Kconfig
+++ b/board/microchip/mpfs_icicle/Kconfig
@@ -50,6 +50,7 @@
 	imply CMD_I2C
 	imply DM_I2C
 	imply SYS_I2C_MICROCHIP
+	imply MTD
 	imply SPI
 	imply DM_SPI
 	imply MICROCHIP_COREQSPI