Improve MSP430 section placement.

Improve MSP430 section placement.

ld	* emultempl/msp430.em (change_output_section): New function.
	(move_prefixed_section): New function.
	(add_region_prefix): New function.
	(msp430_elf_after_open): New function.
	(gld${EMULATION_NAME}_add_options): Implement.
	(gld${EMULATION_NAME}_list_options): Implement.
	(gld${EMULATION_NAME}_handle_option): Implement.
	* ld.texinfo: Document new options.
	* testsuite/ld-msp430-elf/main-bss-lower.d: New.
	* testsuite/ld-msp430-elf/main-bss-upper.d: New.
	* testsuite/ld-msp430-elf/main-const-lower.d: New.
	* testsuite/ld-msp430-elf/main-const-upper.d: New.
	* testsuite/ld-msp430-elf/main-text-lower.d: New.
	* testsuite/ld-msp430-elf/main-text-upper.d: New.
	* testsuite/ld-msp430-elf/main-var-lower.d: New.
	* testsuite/ld-msp430-elf/main-var-upper.d: New.
	* testsuite/ld-msp430-elf/main-with-data-bss-unique-sec.s: New.
	* testsuite/ld-msp430-elf/main-with-data-bss.s: New.
	* testsuite/ld-msp430-elf/main-with-text-rodata-unique-sec.s: New.
	* testsuite/ld-msp430-elf/main-with-text-rodata.s: New.
	* testsuite/ld-msp430-elf/msp430-elf.exp: New.
	* testsuite/ld-msp430-elf/msp430-no-lower.ld: New.
	* testsuite/ld-msp430-elf/msp430.ld: New.
	* emultempl/msp430.em (data_statement_size): New.
	(eval_upper_either_sections): New.
	(eval_lower_either_sections): New.
	(intermediate_relax_sections): New.
	(msp430_elf_after_allocation): New.
	* emultempl/msp430.em (gld${EMULATION_NAME}_place_orphan): Always
	place sections in the lower region.

gas	* config/tc-msp430.c (md_parse_option): Define high data and high
	bss symbols if -mdata-region is passed.
	Define -mdata-region open.
	* doc/c-msp430.texi: Document -mdata-region.
	* testsuite/gas/msp430/high-data-bss-sym.d: New test.
	* testsuite/gas/msp430/high-data-bss-sym.s: New.
	* testsuite/gas/msp430/msp430.exp: Add -mdata-region tests.