cromo: Add ExtractUint32 function

BUG=chromium-os:11879
TEST=use 'modem status' to monitor activation state while activating.
Notice that cromo now reports state 1 --
MM_ACTIVATION_STATE_ACTIVATING

Review URL: http://codereview.chromium.org/6592070

Change-Id: I2ab0da772638d0a7277c829ed01cd34e01d3fe9e
2 files changed