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/arm/Kconfig b/arch/arm/Kconfig
index 86b6e29..2a3a36e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -503,6 +503,7 @@
 config TARGET_BCMCYGNUS
 	bool "Support bcmcygnus"
 	select CPU_V7
+	imply CMD_HASH
 
 config TARGET_BCMNSP
 	bool "Support bcmnsp"