Consistently use CLOCK_MONOTONIC for timing encryption

time_started in encryptGroupsData is set from and compared to
clock_gettime(CLOCK_MONOTONIC, ...) nearly everywhere: "Clock that
cannot be set and represents monotonic time since some unspecified
starting point". However in cryptfs_enable_inplace_f2fs() it is set
from a different clock, time(NULL), with the result that the setprop
calls that indicate progress are wrong and can be called much too
often. The fix is to make this function consistent with
cryptfs_enable_inplace_ext4.

Bug: 146877356
Change-Id: I2707180e5c5bf723a5a880f6a3aac47f2bb34ccd