fb: introduce framebuffer support to Minix

This patch introduces a framebuffer to Minix. It's written for the ARM
port of Minix, but has an architectural split that separates the
hardware dependent part from the non-hardware dependent part. Futhermore,
this driver was developed using a screen that has a native resolution of
1024x600 pixels and having lack of support for obtaining EDID from the
screen. Consequently, it uses a hardcoded resolution of 1024x600.

The driver uses an interface based on the Linux ioctl API, but supports
only a very limited subset.

sys/sys/ioctl.h

@@ -20,6 +20,7 @@
 #include <sys/ioc_memory.h>	/* 'm'			*/
 #include <sys/ioc_tape.h>	/* 'M'			*/
 #include <sys/ioc_sound.h>	/* 's'			*/
+#include <sys/ioc_fb.h>		/* 'F'			*/
 
 #if defined(_NETBSD_SOURCE)
 #define		TIOCDRAIN 	TCDRAIN