power/rk3399: Do not boot until power button is released
power/rk3399: Do not boot until power button is released

This is the expected behavior for tablet/detachable.

BUG=b:119508214
BRANCH=scarlet
TEST=When a dru is off, press VolUP + VolDN + Pwr buttons
for 10 secs without seeing dru boots, and then release those
buttons, confirm dru enters recovery mode.

Change-Id: Ib8d018da2af23a80a644f75808f9ed391b35d0f0
Signed-off-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1336739
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@chromium.org>
Reviewed-by: Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec