input: qpnp-power-on: Add a property to force hard-reset offset

Some (PON gen2) platforms still use legacy hard-reset offset [7:2]
of the PON_RB_SPARE register. Add a DT property to support it.

Change-Id: I8fd3434bcc064965b11aaf3e9c7fcbf694145d21
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>