Rename CACHE_SUPPORT to CACHE

Rename this option so that CONFIG_IS_ENABLED can be used with it.

Oddly there is already an SPL_CACHE option. Drop it in favour of this one.

Drop the special SPL Makefile rule which is now superfluous.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index de0b0e4..533ec90 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -495,7 +495,7 @@
 	  ensure this information is available to the next image
 	  invoked).
 
-config SPL_CACHE_SUPPORT
+config SPL_CACHE
 	bool "Support CACHE drivers"
 	help
 	  Enable CACHE drivers in SPL. These drivers can keep data so that
@@ -808,12 +808,6 @@
 	  README.ubispl for more info.
 
 if SPL_DM
-config SPL_CACHE
-	depends on CACHE
-	bool "Support cache drivers in SPL"
-	help
-	  Enable support for cache drivers in SPL.
-
 config SPL_DM_SPI
 	bool "Support SPI DM drivers in SPL"
 	help