platform: msm_shared: Update pon register bit usage
platform: msm_shared: Update pon register bit usage

PON register bits 2 to 7 are allocated for reboot reasons, update the
reboot driver to use all the bits. Update the reboot reasons to start
with 0x1 and extend when more reboot reasons are added.

Change-Id: I24062d13e904ceaf11d34136a3337749623053b1

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