This change provides an option to add /dev/urandom to all architectures.  The pseudo-random algorithm I choose strikes an arguably-good balance between being "random" and small/fast enough for 8/16 bit MCUs.  It’s the well-documented xorshift128 algorithm.  It has an internal state of 128 bits that can be [re-]seeded with a write.

PTY: Add some encode to reduce the likely of misinterpreting the return value of the file open() method

EXEEXT only needs to be appended once

PTY: Add ioctls to support locking and unlocking of the slave.  LIBC: Add implementation of unlockpt()

PTY: Added PTY IOCTL command definitions.  Add support for TIOCGPTN.  LIB: Implement ptsname() and ptsname_r()

Correct some Make.defs problems for qemu-486 config

Fix a bug of tiva i2c ports configuration

Prototype versions of ptmx/pty suppoprt.  Still under developement; not yet hooked into build or configuration system.

Per documentation SAM4S and SAM4E have the BMR register values
as they are already defined. No need for chip specific values.

In addition:
 - CONFIG_ARCH_CHIP_SAM4s has wrong lower case 's' so the definitions would
   not be used anyways for SAM4S builds.
 - TC_BMR_TC2XC2S_TIOA2 does not make sense. There is no way to loop back
   TC2's TIOA2 into itself.