MSP430: Enable relaxation of relocs in JMP instructions

MSP430: Enable relaxation of relocs in JMP instructions

This patch fixes relocation overflows caused by an inability to relax
unconditional JMP instructions to BR instructions.

bfd/ChangeLog:

2020-02-10  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* elf32-msp430.c (msp430_elf_relax_add_two_words): Rename to
	msp430_elf_relax_add_words. Support insertion of either one or two
	words.
	(msp430_elf_relax_section): Catch opcode of 0x3c00 when relocation
	needs to be grown. Handle insertion of branch instruction to replace
	jump.