MdeModulePkg/Gcd: Check memory allocation when initializing memory

MdeModulePkg/Gcd: Check memory allocation when initializing memory

CoreInitializeMemoryServices was not checking for any existing memory
allocation created in the HOB producer phase. If there are memory
allocations outside of the region covered by the HOB List then Gcd could
select that region for memory which can result in the memory allocation
to not be handled and memory overwrites.

Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>