block: Add SPL_BLOCK_CACHE and default n

When enabling BLOCK_CACHE on devices with limited RAM during SPL,
some devices may not boot.  This creates an option to enable
block caching in SPL by defaults off.  It is dependent on SPL_BLK

Fixes: 46960ad6d0 ("block: Have BLOCK_CACHE default to y in some cases")

Signed-off-by: Adam Ford <aford173@gmail.com>

drivers/block/Kconfig

@@ -37,6 +37,13 @@ config BLOCK_CACHE
 	  it will prevent repeated reads from directory structures and other
 	  filesystem data structures.
 
+config SPL_BLOCK_CACHE
+	bool "Use block device cache in SPL"
+	depends on SPL_BLK
+	default n
+	help
+	  This option enables the disk-block cache in SPL
+
 config IDE
 	bool "Support IDE controllers"
 	select HAVE_BLOCK_DEVICE

drivers/block/Makefile

@@ -11,4 +11,4 @@ endif
 
 obj-$(CONFIG_IDE) += ide.o
 obj-$(CONFIG_SANDBOX) += sandbox.o
-obj-$(CONFIG_BLOCK_CACHE) += blkcache.o
+obj-$(CONFIG_$(SPL_)BLOCK_CACHE) += blkcache.o

include/blk.h

@@ -111,7 +111,7 @@ struct blk_desc {
 #define PAD_TO_BLOCKSIZE(size, blk_desc) \
 	(PAD_SIZE(size, blk_desc->blksz))
 
-#ifdef CONFIG_BLOCK_CACHE
+#if CONFIG_IS_ENABLED(BLOCK_CACHE)
 /**
  * blkcache_read() - attempt to read a set of blocks from cache
  *