libgcc pru: Define TARGET_HAS_NO_HW_DIVIDE

This patch aligns the configuration to the actual PRU capabilities. It
also reduces the size of the affected libgcc functions.

For a real-world project using integer arithmetics the savings
are significant:

  Before:
     text    data     bss     dec     hex filename
     3688     865     544    5097    13e9 hc-sr04-range-sensor.elf

  With TARGET_HAS_NO_HW_DIVIDE defined:
     text    data     bss     dec     hex filename
     2824     865     544    4233    1089 hc-sr04-range-sensor.elf

Execution speed also appears to have improved. The moddi3 function is
now executed in half the CPU cycles.

libgcc/ChangeLog:

	* config/pru/t-pru (HOST_LIBGCC2_CFLAGS): Add
	-DTARGET_HAS_NO_HW_DIVIDE.

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