MdeModulePkg: Change PlatformLogo.GetImage use INTN for minus value

MdeModulePkg: Change PlatformLogo.GetImage use INTN for minus value

The parameter name is also changed from Coordinate* to Offset* to
reflect that it's the offset to the location specified by Attribute.
For example, when the Attribute is Center, OffsetX and OffsetY are
used to specify the offset to the Center. OffsetX = 100 means
100 pixels right to the Center.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18866 6f19259b-4bc3-4df7-8a09-765794883524