arm, at91, spl: add spl support for the taurus board

replaces the at91bootstrap code with SPL code.

make the spl image with:
./tools/mkimage -T atmelimage -d spl/u-boot-spl.bin spl/boot.bin

this writes the length of the spl image into the 6th
execption vector. This is needed from the ROM bootloader.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index bd073eb..ffc89e7 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -207,6 +207,7 @@
 	select CPU_ARM926EJS
 
 config TARGET_TAURUS
+	select SUPPORT_SPL
 	bool "Support taurus"
 	select CPU_ARM926EJS