input: qpnp-power-on: refactor the qpnp-power-on driver

Refactor the qpnp-power-on driver to reduce complexity, improve
readability, and resolve various minor coding concerns.

Change-Id: I27382f07a6ba3e2d0c64aa731393afff27628a36
Signed-off-by: David Collins <collinsd@codeaurora.org>