msm: camera: isp: fix a cts test failure due to framedrop pattern

The ITS HAL3 test failed due to broken frames and green frames. The
root cause of the issue is due to the framedrop pattern setting in the
isp driver. This change fixes the following issues:

a) Keep tracking the hw framedrop pattern even after the reg update ack
miss.

b) Remove a race condition between the framedrop pattern setting and
request frame ioctl handling.

c) Correctly set the framedrop pattern after the request frame.

Change-Id: I862046c718d6e3a28d5f372eb2eb5e371471eb58
Signed-off-by: Jing Zhou <jzhou70@codeaurora.org>