ShellPkg: update ping to use timer service instead of timer arch protocol .

ShellPkg: update ping to use timer service instead of timer arch protocol .

The ping command uses PI CPU arch protocol to calculate the RTT time, which is
not allowed to use in UEFI shell. This patch updates it to use the UEFI timer
event and Stall service to estimate the system timer period.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Hegde, Nagaraj P <nagaraj-p.hegde@hpe.com>