[cloud] Use PCIAPI_DIRECT for cloud images

[cloud] Use PCIAPI_DIRECT for cloud images

The version of SeaBIOS found on some AWS EC2 instances (observed with
t3a.nano in eu-west-1) has no support for the INT 1A PCI BIOS calls.

Bring config/ioapi.h into the named-configuration set of headers, and
specify the use of PCIAPI_DIRECT for CONFIG=cloud, to work around the
missing PCI BIOS support.

Switching to a different named configuration will now unfortunately
cause an almost complete rebuild of iPXE.  As described in commit
c801cb2 ("[build] Allow for named configurations at build time"), this
is the reason why config/ioapi.h was not originally in the
named-configuration set of header files.

This rebuild cost is acceptable given that build times are
substantially faster now than seven years ago, and that very few
people are likely to be switching named configurations on a regular
basis.

Signed-off-by: Michael Brown <mcb30@ipxe.org>