MdeModulePkg SataControllerDxe: Calculate ChannelCount based on PI value

MdeModulePkg SataControllerDxe: Calculate ChannelCount based on PI value

Current code calculates ChannelCount based on CAP(NP) value.
It only works when the ports implemented number are <= CAP(NP),
for example, platform has CAP(NP) = 5 (means 6 ports) and ports
implemented are 0, 1, 2, 3, 4 and 5.

But we have some platform that has CAP(NP) = 1 (means 2 ports) and
ports implemented are 1 and 2, and has no port 0 implemented, then
current code does not work.

This patch updates the code to calculate ChannelCount based on PI value.

Cc: Amy Chan <amy.chan@intel.com>
Cc: Hong-chihX Hsueh <hong-chihx.hsueh@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>
Tested-by: Hong-chihX Hsueh <hong-chihx.hsueh@intel.com>