arch: remove BR2_arm920 reference

The BR2_GCC_TARGET_CPU defines a value for the BR2_arm920 case, but
this option does not exist. Therefore, this commit removes one line of
dead code.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

arch/Config.in.arm

@@ -344,7 +344,6 @@ config BR2_ARCH_HAS_ATOMICS
 	default y
 
 config BR2_GCC_TARGET_CPU
-	default "arm920"	if BR2_arm920
 	default "arm920t"	if BR2_arm920t
 	default "arm922t"	if BR2_arm922t
 	default "arm926ej-s"	if BR2_arm926t