Add VmShmem calculate for getRss

In kernel, /proc/<pid>/status reporting calculates total_rss as:
total_rss = anon + file + shmem
Currently Process.getRss() only returns value of total_rss, anon,
file and swap, without shmem. This patch adds shmem reporting in
getRss(), to provide all components of total_rss calculation.

Bug: 318788245
Signed-off-by:  <xueguolun@xiaomi.corp-partner.google.com>
Change-Id: I7dbb4d00a08e6d93ee77768740f2acab5a58a9ea