Allow EFI and ACPI to be included together. When ACPI is included
first, EFI will use its definitions for {,U}INT{8,16,32,64} and
BOOLEAN. When EFI is included first, define ACPI_USE_SYSTEM_INTTYPES
to tell ACPI that these are already defined.
Differential Revision: https://reviews.freebsd.org/D1905