crossgcc: add armv7a-eabi to list of working toolchains

Change-Id: Ibf221db4ca60d802b460d56f5fcca95ff49fc542
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/2273
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
diff --git a/util/crossgcc/README b/util/crossgcc/README
index e29f5e1..e4a3e42 100644
--- a/util/crossgcc/README
+++ b/util/crossgcc/README
@@ -8,6 +8,7 @@
   x86_64-elf
   powerpc-elf
   mipsel-elf
+  armv7a-eabi
 
 known broken:
   alpha-elf