soc: qcom: spm: Poll for the PMIC_STATE after updating the VCTL register

The PMIC_STATE is expected to move to idle after the VCTL register
value is written to the PMIC.

Also update the PMIC_STATE poll timeout to 500us for all the targets.

CRs-Fixed: 1024714
Change-Id: If9d9875a967179c6ee5fced8f019c01f1a2f0583
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>