Fix AVR assembler so that it creates relocs that will work with linker relaxation.

Fix AVR assembler so that it creates relocs that will work with linker relaxation.

	PR 28686
gas	* config/tc-avr.h (tc_fix_adjustable): Define.
	* config/tc-avr.c (avr_fix_adjustable): New function.
	* testsuite/gas/all/gas.exp: Skip tests that need adjustable fixups.
	* testsuite/gas/elf/elf.exp: Likewise.
	* testsuite/gas/avr/diffreloc_withrelax.d: Adjust expected output.
	* testsuite/gas/avr/pc-relative-reloc.d: Adjust expected output.

ld	* testsuite/ld-avr/avr-prop-7.d: Adjust expected output.
	* testsuite/ld-avr/avr-prop-8.d: Likewise.
	* testsuite/ld-avr/pr13402.d: Likewise.