msm: lpm_levels: remove rpm handshake in l2_gdhs mode

Remove rpm handshake in l2_gdhs mode and adjust the
latency values for l2_gdhs mode. Add a new dt entry to
inform lpm_levels driver to send sleep votes to rpm.

CRs-fixed: 604873
Change-Id: I9eeae5fada4f84ee2ca2eb9d67707dee1adf56ac
Signed-off-by: Anil kumar mamidala <amami@codeaurora.org>