MIPS: Add LUI instruction for mips16e2

MIPS: Add LUI instruction for mips16e2

This patch adds LUI instruction from mips16e2
with corresponding test.

gcc/ChangeLog:

	* config/mips/mips.cc(mips_symbol_insns_1): Generates LUI instruction.
	(mips_const_insns): Same as above.
	(mips_output_move): Same as above.
	(mips_output_function_prologue): Same as above.
	* config/mips/mips.md: Same as above

gcc/testsuite/ChangeLog:

	* gcc.target/mips/mips16e2.c: Add new tests for mips16e2.