tests: acpi: make pointer to RSDP 64bit

tests: acpi: make pointer to RSDP 64bit

In case of UEFI, RSDP doesn't have to be located in lowmem,
it could be placed at any address. Make sure that test won't
break if it is placed above the first 4Gb of address space.

PS:
While at it cleanup some local variables as we don't really
need them.

Signed-off-by: Igor Mammedov <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <1556808723[email protected]>
Reviewed-by: Wei Yang <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>