warp7: Add Kconfig WARP7_ROOT_PART

Adding CONFIG_WARP7_ROOT_PART allows a defconfig to specify which partition
is use as the root partition on WaRP7, this is a desirable change in order
to support a different partitioning schemes. The default is the current
partition #2.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>

board/warp7/Kconfig

@@ -6,6 +6,14 @@ config SYS_BOARD
 config SYS_CONFIG_NAME
 	default "warp7"
 
+config WARP7_ROOT_PART
+	int "Partition number to use for root filesystem"
+	default 2
+	help
+	  The partition number to use for root filesystem this is the
+	  partition that is typically specified with root=/dev/sdaX or
+	  which gets converted into a root=PARTUUID=some_uuid.
+
 config SYS_FDT_ADDR
 	hex "FDT load address"
 	default 0x83000000