PRU: Remove TARGET_HARD_REGNO_CALL_PART_CLOBBERED

PRU: Remove TARGET_HARD_REGNO_CALL_PART_CLOBBERED

Per clarification in [1], macro is supposed to check for partial
clobbering of single HW registers. Since PRU declares only 8-bit
HW registers, and ABI does not define individual bit clobbering,
it is safe to remove the implementation.

[1] https://gcc.gnu.org/ml/gcc-patches/2019-09/msg00778.html

gcc/ChangeLog:

2020-05-05  Dimitar Dimitrov  <dimitar@dinux.eu>

	* config/pru/pru.c (pru_hard_regno_call_part_clobbered): Remove.
	(TARGET_HARD_REGNO_CALL_PART_CLOBBERED): Remove.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>