fs: add CONFIG_BUFFER_HEAD

Add a new config option that controls building the buffer_head code, and
select it from all file systems and stacking drivers that need it.

For the block device nodes and alternative iomap based buffered I/O path
is provided when buffer_head support is not enabled, and iomap needs a
a small tweak to define the IOMAP_F_BUFFER_HEAD flag to 0 to not call
into the buffer_head code when it doesn't exist.

Otherwise this is just Kconfig and ifdef changes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20230801172201.1923299-7-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

freevxfs: Kconfig: fix spelling

Fix a spello in freevxfs Kconfig.
(reported by codespell)

Link: https://lkml.kernel.org/r/20230124181638.15604-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

treewide: Add SPDX license identifier - Makefile/Kconfig

Add SPDX license identifiers to all Make/Kconfig files which:

- Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

freevxfs: update Kconfig information

Signed-off-by: Krzysztof Błaszkowski <kb@sysmikro.com.pl>
Signed-off-by: Christoph Hellwig <hch@lst.de>

freevxfs: update documentation and cresdits for HP-UX support

Signed-off-by: Krzysztof Błaszkowski <kb@sysmikro.com.pl>
[hch: cosmetic updates]
Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/Kconfig: move vxfs out

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>