mmc: Separate "mmc swrite" from fastboot

Introduce CONFIG_IMAGE_SPARSE and CONFIG_CMD_MMC_SWRITE so the "mmc
swrite" command is separated from the fastboot code.

Move image-sparse from common to lib so it's clear it's library code.

Rename CONFIG_FASTBOOT_FLASH_FILLBUF_SIZE to CONFIG_IMAGE_SPARSE_FILLBUF_SIZE
and migrate it to Kconfig.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Acked-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 9848c06..30cf63f 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -833,6 +833,14 @@
 	  Enable the commands for reading, writing and programming the
 	  key for the Replay Protection Memory Block partition in eMMC.
 
+config CMD_MMC_SWRITE
+	bool "mmc swrite"
+	depends on CMD_MMC && MMC_WRITE
+	select IMAGE_SPARSE
+	help
+	  Enable support for the "mmc swrite" command to write Android sparse
+	  images to eMMC.
+
 config CMD_NAND
 	bool "nand"
 	default y if NAND_SUNXI