[boot/efi] scan all display modes rather than sequential try-fail way
This patch allows to scan all display modes in boot1 as loader does.
Before system tried to select optimal display mode by sequential scan of
modes and if error then stop scanning. This way is not good, because
if mode N is not present, mode N+1 may exist.
In loader we use conout->Mode->MaxMode to identify maximum number of modes.
This commit is to use same way in boot1 as in loader.
Reported by: Andrey Pustovetov <email@example.com>
Reviewed by: tsoome
Differential Revision: https://reviews.freebsd.org/D13541