Print symbol names in comments for LDS/STS disassembly.

Print symbol names in comments for LDS/STS disassembly.

This patch adds default data address space origin (0x800000) to the symbol addresses.
when disassemble lds/sts instructions. So that symbol names shall be printed in comments
for lds/sts instructions disassemble.

ld/
	* testsuite/ld-avr/lds-mega.d: New test.
	* testsuite/ld-avr/lds-mega.s: New test source.
	* testsuite/ld-avr/lds-tiny.d: New test.
	* testsuite/ld-avr/lds-tiny.s: New test source.

opcodes/
	* avr-dis.c (avr_operand): Add default data address space origin (0x800000) to the
	address and set as symbol address for LDS/ STS immediate operands.