MIPS: Use ISA_HAS_9BIT_DISPLACEMENT for mips16e2

MIPS: Use ISA_HAS_9BIT_DISPLACEMENT for mips16e2

The MIPS16e2 ASE has PREF, LL and SC instructions,
they use 9 bits immediate, like mips32r6.
The MIPS32 PRE-R6 uses 16 bits immediate.

gcc/ChangeLog:

	* config/mips/mips.h(ISA_HAS_9BIT_DISPLACEMENT): Add clause
	for ISA_HAS_MIPS16E2.
	(ISA_HAS_SYNC): Same as above.
	(ISA_HAS_LL_SC): Same as above.