<linux/mod_devicetable.h> is included transitively in nearly every
driver in an x86_64 allmodconfig build of v7.1:

	$ find drivers -name \*.o -not -name \*.mod.o | wc -l
	21330
	$ find drivers -name \*.o.cmd -not -name \*.mod.o.cmd | xargs grep -l mod_devicetable.h | wc -l
	17038

The result is that even when touching an obscure device id struct most
of the kernel needs to be recompiled. Given that each driver typically
only needs one or two of these structures, splitting into per subsystem
headers and only including what is really needed reduces the amount of
needed recompilation.

Implement the first step and define each device id struct in a separate
header (together with its associated #defines).

<linux/mod_devicetable.h> is modified to include all the new headers to
continue to provide the same symbols.

Several headers currently include <linux/mod_devicetable.h>, those that
are most lukrative to include only their subsystem headers only are:

	$ git -C source grep -l mod_devicetable.h include/linux | while read h; do echo -n "$h:"; find drivers -name \*.o.cmd -not -name \*.mod.o.cmd | xargs grep -l $h | wc -l; done | sort -t: -k2 -n -r | head
	include/linux/of.h:10897
	include/linux/pci.h:7920
	include/linux/acpi.h:7097
	include/linux/i2c.h:5402
	include/linux/spi/spi.h:1897
	include/linux/dmi.h:1643
	include/linux/usb.h:1222
	include/linux/input.h:1205
	include/linux/mdio.h:835
	include/linux/phy.h:733

struct cpu_feature isn't really a device_id struct. That is kept in
<linux/mod_devicetable.h> for now.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # zorro
Link: https://patch.msgid.link/41400e323be8640702b906d04327e833c5bdaf4a.1782808461.git.u.kleine-koenig@baylibre.com
[Drop "MOD" from the header guards]
Signed-off-by: Uwe Kleine-König (The Capable Hub) <u.kleine-koenig@baylibre.com>