Add basic support for FDT to i386 & amd64. This change includes:
1.  Common headers for fdt.h and ofw_machdep.h under x86/include
    with indirections under i386/include and amd64/include.
2.  New modinfo for loader provided FDT blob.
3.  Common x86_init_fdt() called from hammer_time() on amd64 and
    init386() on i386.
4.  Split-off FDT specific low-level console functions from FDT
    bus methods for the uart(4) driver. The low-level console
    logic has been moved to uart_cpu_fdt.c and is used for arm,
    mips & powerpc only. The FDT bus methods are shared across
    all architectures.
5.  Add dev/fdt/fdt_x86.c to hold the fdt_fixup_table[] and the
    fdt_pic_table[] arrays. Both are empty right now.

FDT addresses are I/O ports on x86. Since the core FDT code does
not handle different address spaces, adding support for both I/O
ports and memory addresses requires some thought and discussion.
It may be better to use a compile-time option that controls this.

Obtained from:	Juniper Networks, Inc.