Add dev firmware key to devkeys.

The existing keys are kept the same, so that old dev kernels and
firmware remain compatible with new kernels and firmware.

Change-Id: I4177d1868904a477d79b9f2e6de88ed756ed57b4

BUG=chrome-os-partner:2218
TEST=manual:

Build firmware with new keys.

Boot with dev switch on.
Run 'crossystem mainfw_act mainfw_type'.
Should see "A developer"

Boot with dev switch off.
Run 'crossystem mainfw_act mainfw_type'.
Should see "B normal"

Review URL: http://codereview.chromium.org/6580035

tests/devkeys/create_new_keys.sh

@@ -94,6 +94,7 @@ function make_keyblock {
 # Create the normal keypairs
 make_pair root_key                 11
 make_pair firmware_data_key        7
+make_pair dev_firmware_data_key    7
 make_pair kernel_subkey            7
 make_pair kernel_data_key          4
 
@@ -106,6 +107,9 @@ make_pair installer_kernel_data_key 11
 # since it's never even checked during Recovery mode.
 make_keyblock firmware 7 firmware_data_key root_key
 
+# Create the dev firmware keyblock for use only in Developer mode.
+make_keyblock dev_firmware 6 dev_firmware_data_key root_key
+
 # Create the recovery kernel keyblock for use only in Recovery mode.
 make_keyblock recovery_kernel 11 recovery_kernel_data_key recovery_key