ARM: at91/trivial: update Kconfig comment to mention SAMA5

Cortex-A5 SAMA5 processors were not listed, add this in the AT91 comment.
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: NBoris BREZILLON <boris.brezillon@free-electrons.com>

arch/arm/Kconfig

@@ -380,7 +380,7 @@ config ARCH_AT91
 	select USE_OF
 	help
 	  This enables support for systems based on Atmel
-	  AT91RM9200 and AT91SAM9* processors.
+	  AT91RM9200, AT91SAM9 and SAMA5 processors.
 
 config ARCH_CLPS711X
 	bool "Cirrus Logic CLPS711x/EP721x/EP731x-based"