MdeModulePkg/BdsDxe: Update BdsEntry to use Variable Policy

MdeModulePkg/BdsDxe: Update BdsEntry to use Variable Policy

Changed BdsEntry.c to use Variable Policy instead of Variable Lock
as Variable Lock will be Deprecated eventually

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Signed-off-by: Kenneth Lautner <kenlautner3@gmail.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>