reset: qcom-pon: Add support for gen2 pon

Add support for gen2 pon register so "reboot bootloader" can
work on pixel3 and db845.

Cc: Andy Gross <agross@kernel.org>
Cc: David Brown <david.brown@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: devicetree@vger.kernel.org
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>

v2:
* Split out dts changes into separate path
* Minor cleanups and remove unused variables

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>