PR27290, PR27293, PR27295, various avr objdump fixes

PR27290, PR27293, PR27295, various avr objdump fixes

Adds missing sanity checks for avr device info note, to avoid
potential buffer overflows.  Uses bfd_malloc_and_get_section for
sanity checking section size.

	PR 27290
	PR 27293
	PR 27295
	* od-elf32_avr.c (elf32_avr_get_note_section_contents): Formatting.
	Use bfd_malloc_and_get_section.
	(elf32_avr_get_note_desc): Formatting.  Return descsz.  Sanity
	check namesz.  Return NULL if descsz is too small.  Ensure
	string table is terminated.
	(elf32_avr_get_device_info): Formatting.  Add note_size param.
	Sanity check note.
	(elf32_avr_dump_mem_usage): Adjust to suit.