nios2: Add CDX support

Add support for the CDX Code Density Extensions present in
Nios II R2 . This introduces new 16bit instruction set to
improve code density while retaining support for the 32bit
Nios II R2 instructions.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Ley Foon Tan <lftan@altera.com>

arch/nios2/platform/Kconfig.platform

@@ -90,6 +90,15 @@ config NIOS2_BMX_SUPPORT
 	  the BMX Bit Manipulation Extension instructions. Enables
 	  the -mbmx compiler flag.
 
+config NIOS2_CDX_SUPPORT
+	bool "Enable CDX instructions"
+	depends on NIOS2_ARCH_REVISION = 2
+	default n
+	help
+	  Set to true if you configured the Nios II R2 to include
+	  the CDX Bit Manipulation Extension instructions. Enables
+	  the -mcdx compiler flag.
+
 config NIOS2_FPU_SUPPORT
 	bool "Custom floating point instr support"
 	default n