Convert CONFIG_CMD_HASH to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_HASH

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Rework slightly, enable on some boards again]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 01e9008..3d2c131 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -33,6 +33,7 @@
 	select SYS_FSL_DDR
 	select SYS_FSL_DDR_BE
 	imply USB_EHCI_HCD if USB
+	imply CMD_HASH
 
 config MPC86xx
 	bool "MPC86xx"