Fix wrong information of TigerLake in Readme.md

Machine Name of TigerLake is TGL-U DDR4 RVP but no TGL-U LPDDR4 RVP

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3175



Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Signed-off-by: Heng Luo <heng.luo@intel.com>
Reviewed-by: Sai Chaganty <rangasai.v.chaganty@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>