MFC r277454, r277460, r277465, r277466, r277467, r277469, r277470, r277471,
r277472, r277473, r277474, r277475, r277476, r277477, r277478, r277479,
r277480, r277512, r277516:

Add inline implementations of arm bus_space_read/write_N().

Revise the arm bus_space implementation to avoid dereferencing the tag on
every operation to retrieve the bs_cookie value almost nothing actually uses.

Use the explicit member initializer style to init the bus_space struct.

Use arm/bus_space-v6.c for all armv6 systems

Consolidate many identical implementations of bus_space to a single
common tag and implementation shared by armv4 and armv6.

Micro-optimize the new arm inline bus_space implementation by grouping all
the data the inline functions access together at the start of the bus_space
struct so that they all fit in a single cache line.

MFC r277454, r277460, r277465, r277466, r277467, r277469, r277470, r277471,
r277472, r277473, r277474, r277475, r277476, r277477, r277478, r277479,
r277480, r277512, r277516:

Add inline implementations of arm bus_space_read/write_N().

Revise the arm bus_space implementation to avoid dereferencing the tag on
every operation to retrieve the bs_cookie value almost nothing actually uses.

Use the explicit member initializer style to init the bus_space struct.

Use arm/bus_space-v6.c for all armv6 systems

Consolidate many identical implementations of bus_space to a single
common tag and implementation shared by armv4 and armv6.

Micro-optimize the new arm inline bus_space implementation by grouping all
the data the inline functions access together at the start of the bus_space
struct so that they all fit in a single cache line.