IntelFsp2Pkg/FspSecCore: Make FSP functions position independent

IntelFsp2Pkg/FspSecCore: Make FSP functions position independent

The current AsmGetFspInfoHeader function in FspHeader.nasm is
position dependent code since it uses absolute address. Change
to use relative address instead to make it position independent.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Maurice Ma <maurice.ma@intel.com>
Reviewed-by: Giri P Mudusuru <giri.p.mudusuru@intel.com>