block: Have BLOCK_CACHE default to y in some cases

When dealing with filesystems that come from block devices we can get a
noticeable performance gain in some use cases from having the block
cache enabled.  The code paths are valid in other cases when we have BLK
set and may provide wins in raw reads in some use cases, so have this be
default when BLK is enabled.

Signed-off-by: Tom Rini <trini@konsulko.com>

drivers/block/Kconfig

@@ -29,7 +29,8 @@ config SPL_BLK
 
 config BLOCK_CACHE
 	bool "Use block device cache"
-	default n
+	depends on BLK
+	default y
 	help
 	  This option enables a disk-block cache for all block devices.
 	  This is most useful when accessing filesystems under U-Boot since