power: qpnp-smbcharger: optimize HVDCP 2.0 efficiency

At 9V, the smbcharger is more efficient at a switching frequency of
1MHz. Switch to this when the driver detects that it is in HVDCP 2.0
mode. Also, switch the VFIX clamping voltage threshold so that the
frequency is maintained.

CRs-Fixed: 910651
Change-Id: I4b8e1d360fe301671e882f20b2460cdb737204b0
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>