hvmloader: reinstate datastructure shared with DSDT in SeaBIOS case.

hvmloader: reinstate datastructure shared with DSDT in SeaBIOS case.

I mistakenly thought that the "struct bios_info" was a ROMBIOS
specific data structure and so caused it to be populated only in the
ROMBIOS case.

However it turns out that the majority of the struct's fields are
actually referenced from the ACPI DSDT and hence are needed for
SeaBIOS too.

While in principal it might have been possible to continue to mix
ROMBIOS and ACPI bits in this datastructure this is, evidently,
confusing but also leads to header file dependencies from
ROMBIOS->hvmloader which I had been hoping to avoid so as to head-off
future accidental re-entanglement of ROMBIOS and hvmloader.

So instead I have split the ACPI parts into a new "struct acpi_info"
which is defined entirely within the acpi building code in hvmloader
and which comes with a big comment pointing to the DSDT interaction.

This new ACPI info is placed at 0x9F000 which is available under both
ROMBIOS and SeaBIOS. This address is in a reserved region of the E820
and is just above the ROMBIOS stack.

The resulting "struct rombios_info" is hardly worthy of its own
structure but keep it anyway.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>