Boost init priority before main loop

Now we have more things e.g. loading kernel modules, initialize
selinux. And before all these, system cannot make further progress. It
should be beneficial to boost this critical peroid in init.

Benchmark on a Pixel device shows this saves 100+ms on early boot

ToT release + This CL (P15538587)
D/BaseBootTest: init_stage_second_START_TIME_avg : 1563.4
D/BaseBootTest: ueventd_Coldboot_avg : 219.0
D/BaseBootTest: action_init_/system/etc/init/hw/init.rc:114_START_TIME_avg : 2103.7

ToT release (6654154)
D/BaseBootTest: init_stage_second_START_TIME_avg : 1639.0
D/BaseBootTest: ueventd_Coldboot_avg : 238.2
D/BaseBootTest: action_init_/system/etc/init/hw/init.rc:114_START_TIME_avg : 2226.0

Bug: 143857500
Bug: 147997403
Bug: 160271169
Bug: 160696502
Test: Boottime
Signed-off-by: Wei Wang <wvw@google.com>
Change-Id: I21c9e051f4ae3e953d991c031f151b2779702548