[MTD] User interface to Protection Registers

This is implemented using a ioctl to switch the MTD char device into
one of the different OTP "modes", at which point read/write/seek can
operate on the selected OTP area.  Also some extra ioctls to query
for size and lock protection segments or groups.  Some example user
space utilities are provided.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>