* partmap/gpt.c: Include `<grub/gpt_partition.h>'.
(grub_gpt_partition_type_empty): Redefine with macro from
`<grub/gpt_partition.h>'.
(gpt_partition_map_iterate): Adjust partition type comparison.
Export `entry' as partmap-specific `part.data' struct.
(grub_gpt_header, grub_gpt_partentry): Move from here ...
* include/grub/gpt_partition.h (grub_gpt_header)
(grub_gpt_partentry): ... to here (new file).
* util/i386/pc/grub-setup.c: Include `<grub/gpt_partition.h>'.
(grub_gpt_partition_type_bios_boot): New const variable, defined
with macro from `<grub/gpt_partition.h>'.
(setup): Replace `first_start' with `embed_region', which keeps
track of the embed region (and is partmap-agnostic).
Replace find_first_partition_start() with find_usable_region(),
which finds a usable region for embedding using partmap-specific
knowledge (supports PC/MSDOS and GPT).
Fix all assumptions that the embed region start at sector 1, using
`embed_region.start' from now on. Similarly, use `embed_region.end'
rather than `first_start' to calculate available size.
In grub_util_info() message, replace "into after the MBR" with an
indication of the specific sector our embed region starts at.