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/mach-exynos/Kconfig b/arch/arm/mach-exynos/Kconfig
index 24cb99e..5b6c5ea 100644
--- a/arch/arm/mach-exynos/Kconfig
+++ b/arch/arm/mach-exynos/Kconfig
@@ -18,6 +18,7 @@
 	select CPU_V7
 	select BOARD_EARLY_INIT_F
 	select SHA_HW_ACCEL
+	imply CMD_HASH
 	help
 	  Samsung Exynos5 SoC family are based on ARM Cortex-A15 CPU (and
 	  Cortex-A7 CPU in big.LITTLE configuration). There are multiple SoCs