ARM: at91/trivial: unify functions and machine names

Remove the string "(Device Tree)" after the machine name because all AT91
machines use the DT nowadays.
Also change some function names to unify following the convention:
- at91sam9xxx aren't named sam9, 9xxx but with the full name
- sama5 are the ones that don't have the at91 prefix anymore.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>