arch/arm: remove OABI option

OABI is more than legacy, it's dead.

New developments should go with EABI, since it so much better.
>From the Debian EABI page [0] :
  - floating point performance, with or without an FPU is very much faster
  - mixing soft and hardfloat code is possible
  - structure packing is not as painful as it used to be
  - a more efficient syscall convention
  - more compatibility with various tools

[0] http://wiki.debian.org/ArmEabiPort

[Thomas: keep the ABI choice, as we are going to introduce EABIhf later].
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

arch/Config.in.arm

@@ -72,19 +72,12 @@ choice
 	help
 	  Application Binary Interface to use
 
-	  Note:
-	    Using OABI is discouraged.
-
 config BR2_ARM_EABI_CHOICE
 	bool "EABI"
-config BR2_ARM_OABI
-	bool "OABI"
-	depends on !BR2_GCC_VERSION_4_7_X
 endchoice
 
 config BR2_ARM_EABI
 	def_bool y
-	depends on !BR2_ARM_OABI
 
 config BR2_ARM_ENABLE_NEON
 	bool "Enable NEON SIMD extension support"