ARM: dts: msm: Early init changes for vendor image on msm8996

For use with A/B partition feature, remove early mount of system
image.  Change fs mgr flags from verify to slotselect.
System image is to be mounted in the lk when enabling A/B.

Change-Id: I4fc2ac5f5bd22dea2fd6ff832cd31d1f3697b4d4
Signed-off-by: Anthony Mah <amah@codeaurora.org>