platform: qpnp-power-on: Clear WARM_RESET reason registers

On some targets there is a hardware feature to catch resets
which are not triggered by the MSM. In such cases the warm
reset registers can give a wrong reset reason as they are
not cleared across MSM resets. Avoid this by clearing these
registers after the HLOS has booted up. Also, prior to clearing
them store the last value of these registers for runtime usage.

Add a DT property which controls clearing of these registers.

CRs-Fixed: 713011
Change-Id: Ia806c521f28a5ad1f480236baa6b4cac0359bf62
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>