SAM3/4 Timer: Remove broken definitions for BMR register.

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.