PCI: autoconfig: Don't allocate 64-bit addresses to 32-bit only resources

Currently, if we happen to allocate an address requiring 64 bits to a
device only supporting 32-bit BARs, the address eventually gets silently
truncated to 32 bits. Avoid this by adding a new flag to
pciauto_region_allocate() to bail out in such situations.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Reviewed-by: Simon Glass <sjg@chromium.org>