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/configs/taurus_defconfig b/configs/taurus_defconfig
index 9870048..438e25d 100644
--- a/configs/taurus_defconfig
+++ b/configs/taurus_defconfig
@@ -1,3 +1,4 @@
+CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20,MACH_TYPE=2067,BOARD_TAURUS"
-CONFIG_ARM=y
-CONFIG_TARGET_TAURUS=y
++S:CONFIG_ARM=y
++S:CONFIG_TARGET_TAURUS=y