Since QEMU 2.1, we are allocating more space for ACPI tables, so no
space is left after initrd for the BIOS to allocate memory.

Besides ACPI tables, there are a few other uses of high memory in
SeaBIOS: SMBIOS tables and USB drivers use it in particular.  These uses
allocate a very small amount of memory.  Malloc metadata also lives
there.  So we need _some_ extra padding there to avoid initrd breakage,
but not much.

John Snow found a case where RHEL5 was broken by the recent change to
ACPI_TABLE_SIZE; in his case 4KB of extra padding are fine, but just to
be safe I am adding 32KB, which is roughly the same amount of padding
that was left by QEMU 2.0 and earlier.

Move initrd to leave some space for the BIOS.

Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: John Snow <jsnow@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>