[Patch, avr] Use symbols for MEMORY region lengths if available

[Nicholas Clifton]

Hi Senthil,

> ld/ChangeLog
>
> 2015-02-02  Senthil Kumar Selvaraj<senthil_kumar.selvaraj@atmel.com>
>
> 	* scripttempl/avr.sc: Add new user_signatures region. Define and Use
> 	symbols for all region lengths.
> 	* scripttempl/avrtiny.sc: Define and use symbols for all region lengths.
>
> ld/testsuite/ChangeLog
>
> 2015-02-02  Senthil Kumar Selvaraj<senthil_kumar.selvaraj@atmel.com>
>
> 	* ld-avr/region_overflow.d: New test.
> 	* ld-avr/region_overflow.s: Likewise.
>

Approved and applied.

Cheers
   Nick