Allow whitspace to appear between device name and unit number in loaderdev.
This allows the same value to be used in u-boot commands and the loaderdev
env var that gets passed to ubldr, for example 'fatload mmc 1 ${bootfile}".
Switch zfsboot installer force 4K option to use vfs.zfs.min_auto_ashift=12

Previously we used gnop(8) to fake 4K sector size disks but ZFS now has a
sysctl to control this when creating new top level vdev's so use that
instead.

Differential Revision:	D566
MFC after:	1 month
Sponsored by:	Multiplay
Further reduce the diff between the arm_intrng gic driver and the version
in head.
Remove a volatile qualifier on return type that is ignored and results in
a -Wreturn-type warning when compiled with gcc.
Eliminate a redundant declaration.
Eliminate a "cast discards qualifiers" warning when building with gcc.
Pull out the fdt mapping code into intr.c. The arm_intrng branch also
defines this function allowing the mapping method to change when we move
to it.
Fix the unwinder to get past functions with no stack but may cause an
exception. In this case no registers will be updated but the link register
will be copied to the program counter to be used to find the calling
function. In this case the program counter may be updated and we should
continue with the trace.
sh: Remove EXP_REDIR.

EXP_REDIR was supposed to generate pathnames in redirection if exactly one
file matches, as permitted but not required by POSIX in interactive mode. It
is unlikely this will be implemented.

No functional change is intended.

MFC after:	1 week