MFC r307518:
Fix device delete child function.

When detaching device trees parent devices must be detached prior to
detaching its children. This is because parent devices can have
pointers to the child devices in their softcs which are not
invalidated by device_delete_child(). This can cause use after free
issues and panic().

Device drivers implementing trees, must ensure its detach function
detaches or deletes all its children before returning.

While at it remove now redundant device_detach() calls before
device_delete_child() and device_delete_children(), mostly in
the USB controller drivers.

Tested by: Jan Henrik Sylvester <me@janh.de>
Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D8070

MFC r303891, r303892:
sys: replace comma with semicolon when pertinent.

Uses of commas instead of a semicolons can easily go undetected. The comma
can serve as a statement separator but this shouldn't be abused when
statements are meant to be standalone.

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 r266969 and r276717:
Add 64-bit DMA support in the XHCI controller driver.
- Fix some comments and whitespaces while at it.
- Add support for PAE.

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 r266969 and r276717:
Add 64-bit DMA support in the XHCI controller driver.
- Fix some comments and whitespaces while at it.
- Add support for PAE.