SbsaQemu: Fix numerous SSDT generation problems

1 - The SBSAQEMU_ACPI_ITOA contained a typo that put bogus characters
in the name if number of CPUs was greater than 10. It is safer to use
the AsciiSPrint function from PrintLib.

2 - The _UID fields were bogus, and indicated as bytes in AML instead of
a word. This caused extra Zeros to appear in disassembly. Fixed by
making them AML_WORD_PREFIX and putting CpuId in little endian.

3 - The table was a number of bytes too long, which causes bogus Zero in
dissassembly at end of table. Re-adjust code slightly to reduce table
size once we know the size of the length field.

Signed-off-by: Graeme Gregory <graeme@nuviainc.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>