sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

gpiokeys: Use the new device-tree vendor include

Add gpiokeys driver

gpiokey driver implements functional subset of gpiokeys device-tree bindings:
https://www.kernel.org/doc/Documentation/devicetree/bindings/input/gpio-keys.txt

It acts as a virtual keyboard, so keys are visible through kbdmux(4)

Driver maps linux scancodes for most common keys to FreeBSD scancodes and
also extends spec by introducing freebsd,code property to specify
FreeBSD-native scancodes.

Reviewed by: mmel, jmcneill
Differential Revision: https://reviews.freebsd.org/D6279