ARM: at91: remove AT91X40 macro since it is not use any more

The at91x40.h is not exist. So we remove it.
Signed-off-by: NJosh Wu <josh.wu@atmel.com>
Signed-off-by: NAndreas Bießmann <andreas.devel@googlemail.com>

arch/arm/include/asm/arch-at91/hardware.h

@@ -25,8 +25,6 @@
 # include <asm/arch/at91sam9x5.h>
 #elif defined(CONFIG_AT91CAP9)
 # include <asm/arch/at91cap9.h>
-#elif defined(CONFIG_AT91X40)
-# include <asm/arch/at91x40.h>
 #elif defined(CONFIG_SAMA5D3)
 # include <asm/arch/sama5d3.h>
 #else