platform: msm_shared: Updates to verified boot

 * Verify boot.img with oem keystore (green state)
 * If verification fails with oem keystore use public key
   from certificate embedded in boot.img for verification
   (yellow state)
 * Boot with failed verification state (red state) if green
   and yellow states fail
 * Remove user keystore and verify flash allowed functions
 * Do not assert when verified boot is enabled

Change-Id: Ic740696e89b62321eb59cb9f4d6730f472047c72
3 files changed