BaseTools: Convert string value of void* pcd in command line to array.

BaseTools: Convert string value of void* pcd in command line to array.

For void* type pcd in command line, if its value is string, then
convert the string value to array format. For example,
build --pcd gUefiOvmfPkgTokenSpaceGuid.PcdTest="c",
convert the pcd value from "c" to "{0x63,0x00}".

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: ZhiqiangX Zhao <zhiqiangx.zhao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>