ARM: at91: rename board-dt to more specific name board-dt-sam9

We will produce a board-dt file per SoC core type. That will ease code
readability and will prevent from including superfluous code for supporting
machines that will never be compiled together (particularly the ARM9 and C-A5
upcoming SoCs).

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
[nicolas.ferre@atmel.com: modify commit message]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/arch/arm/configs/at91sam9g20_defconfig b/arch/arm/configs/at91sam9g20_defconfig
index 3b18810..892e828 100644
--- a/arch/arm/configs/at91sam9g20_defconfig
+++ b/arch/arm/configs/at91sam9g20_defconfig
@@ -22,7 +22,7 @@
 CONFIG_MACH_GSIA18S=y
 CONFIG_MACH_USB_A9G20=y
 CONFIG_MACH_SNAPPER_9260=y
-CONFIG_MACH_AT91SAM_DT=y
+CONFIG_MACH_AT91SAM9_DT=y
 CONFIG_AT91_PROGRAMMABLE_CLOCKS=y
 # CONFIG_ARM_THUMB is not set
 CONFIG_AEABI=y