build_image,cros_make_image_bootable: fix missing arm argument

Adds arm_extra_bootargs to boot.desc and to cros_make_image_bootable.

TEST=tegra2 dev-board build_packages, build_image --fast worked
BUG=broken tree

Change-Id: Ifdfeda66f1eb5e5b1e618706eeba269f31fa9913

Review URL: http://codereview.chromium.org/3069031

bin/cros_make_image_bootable

@@ -80,6 +80,9 @@ DEFINE_integer verity_max_ios 1024 \
 DEFINE_string verity_algorithm "sha1" \
   "Cryptographic hash algorithm used for kernel vboot."
 
+DEFINE_string arm_extra_bootargs "" \
+  "Additional command line options to pass to the ARM kernel."
+
 DEFINE_string keys_dir "/usr/share/vboot/devkeys" \
   "Directory containing the signing keys."
 

build_image

@@ -304,6 +304,7 @@ create_boot_desc() {
   --verity_algorithm="${FLAGS_verity_algorithm}"
   --keys_dir="${DEVKEYSDIR}"
   --usb_disk="${FLAGS_usb_disk}"
+  --arm_extra_bootargs="${FLAGS_arm_extra_bootargs}"
   --nocleanup_dirs
   ${enable_rootfs_verification_flag}
 EOF