ueventd: the parallel restorecon dirs is configurable [1/1]

PD#SWPL-45884
BUG:187441275

Problem:
ueventd: coldboot took too much time

Solution:
1.The parallel restorecon dirs can be configured in ueventd.rc
2.Add 'parallel_restorecon_dir' keywords
parallel_restorecon_dir <directory>

Verify:
redi

Change-Id: Id5b13f18d36afb894891697f21ac63e78b3fe130
Signed-off-by: yuehu mi <yuehu.mi@amlogic.com>