PayloadEntry should not assume PcdSystemMemoryUefiRegionSize bytes of memory after the Payload image can be used

[niruiyu]

[niruiyu]

PayloadEntry uses this range of memory to build a new HOB list, based on the information stored in the old HOB list created by boot loader.

I guess the boot loader may creates HOBs in one format but payload expects HOBs in another format. Payload entry is the one that does the HOB convert.

In fact, if the boot loader can directly create the HOBs in final format, payload entry can avoid using the PcdSystemMemoryUefiRegionSize for new HOB creation.

Further checking the implementation, I found PayloadEntry also needs memory to load DXE Core. Anyway, if memory is required by PayloadEntry, better to update the spec to explicitly mention this range.