IntelFsp2Pkg: Skip loading Microcode if MicrocodeCodeSize is zero

IntelFsp2Pkg: Skip loading Microcode if MicrocodeCodeSize is zero

During asm to Nasm conversion, we missed the code to skip loading the
microcode and return success if the size is zero. Added additional check to
report error if the microcode size is not zero but less than 2 kB.

Cc: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Satya Yarlagadda <satya.p.yarlagadda@intel.com>
Reviewed-by: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>