spl: blk: Support loading images from fs

Add a generic API to support loading of SPL payload from any supported
filesystem on a given partition of a block device.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index ae0d507..865571d 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1268,6 +1268,7 @@
 	depends on BLK
 	select HAVE_BLOCK_DEVICE
 	select FS_LOADER
+	select SPL_BLK_FS
 	help
 	  This option enables support for NVM Express devices.
 	  It supports basic functions of NVMe (read/write).