pflash: fix erase command when using mtd backend

The libflash mtd backend lacked support for full-chip erase so it did
not work.  This patch adds that support to libflash. Patch is on it's
way upstream[1].

Note: the old MMIO access method could perform a wole-chip
erase on SPI NOR parts that supported it. This was sometimes a fraction
faster than erasing each page one-by-one when re-flashing the entire
chip.

The mtd API does not (yet) provide a userspace API for that, so libflash
always erases the flash one page at a time. This means you are better
off using the -e command over -E.

Fixes: openbmc/openbmc#747

[1] http://patchwork.ozlabs.org/patch/691765/

Change-Id: I20cf50e70a8487edc8cd77d41e73832913237b1b
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/common/recipes-bsp/skiboot/skiboot.inc b/common/recipes-bsp/skiboot/skiboot.inc
index 248e13f..fa30f09 100644
--- a/common/recipes-bsp/skiboot/skiboot.inc
+++ b/common/recipes-bsp/skiboot/skiboot.inc
@@ -3,6 +3,7 @@
 
 SRC_URI += "git://github.com/open-power/skiboot.git;nobranch=1"
 SRC_URI += "file://0001-external-Use-more-standard-PREFIX-vs-prefix.patch"
+SRC_URI += "file://0002-external-common-Teach-ARM-code-to-erase-mtd-chips.patch"
 
 FILESEXTRAPATHS_append := "${THISDIR}/skiboot:"