rotate is now an angle

fbtft previously used the rotation values 0-3. This was how fbcon did it.

include/uapi/linux/fb.h has this to say:
__u32 rotate;                   /* angle we rotate counter clockwise */
write_cmd() and write_data() is not needed anymore
fbtft_device: no need to distinguish between adafruit18 red and black tab
fbtft: removed comment
add parameters to update_display() and write_vmem()

This is done to decouple par->dirty_lines_{start,end} from these functions
fbtft: protect dirty_lines_{start,end} with a lock

Fixes #1
fbtft: return to dev_warn() since bug is fixed
fbtft: added missing includes for 3.10

The code was relying on other includes to the job. Bad practice.