Maintainers.txt: update UEFI payload information

Remove CorebootModulePkg and CorebootPayloadPkg, and add
UefiPayloadPkg to reflect recently change in UEFI payload.
wiki link for UefiPayloadPkg would be available soon.

Signed-off-by: Guo Dong <guo.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Maurice Ma <maurice.ma@intel.com>