MdeModulePkg: Extend PcdSerialClockRate to dynamic type
MdeModulePkg: Extend PcdSerialClockRate to dynamic type

So it could allow platform module to change the serial clock rate per different hardware.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Feng Tian <feng.tian@intel.com>

git-svn-id: 3158a46dfd52e07d1fda3e32e1ab2e353a00b20f@17606 6f19259b-4bc3-4df7-8a09-765794883524

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2