Clarify the address and pointer conversions on AVR.

Clarify the address and pointer conversions on AVR.

This patch adds additional comments about the conversion of addresses to
pointers and vice-versa on AVR.

Special conversion needs to be done when dealing with an address in the
flash address space, where both code and read-only data can be stored.
Code and data pointers to flash are not addressed the same way:

A code pointer is 16 bit addressed.  A data pointer is 8 bit addressed,
even if the data is in flash.

2014-07-25  Pierre Langlois  <pierre.langlois@embecosm.com>

	* avr-tdep.c (avr_address_to_pointer): Clarify the conversion in the
	comments.
	(avr_pointer_to_address): Likewise.