Clear TPM if software firmware WP is disabled

Change-Id: I98d111d70e777b616cb2d09ec7e2b5d982f3a91e

R=bleung@chromium.org
BUG=chrome-os-partner:3317
TEST=manual

Install R12 release with kernel version 0x00020001.
Run `crossystem tpm_kernver` to verify kernel version.
Run `flashrom --p internal:bus=spi --wp-status` to verify software WP disabled
Run R11 factory install shim
After install finishes, boot to root shell
Run `crossystem tpm_kernver` to verify kernel version is now 0x00010001

Review URL: http://codereview.chromium.org/6840031
1 file changed