sunxi: Kconfig consolidation and cleanup

This series consolidates some Kconfig options and makes SPL_FEL a first class .config member instead of putting it in CONFIG_SYS_EXTRA_OPTIONS.

This means it is possible to do a FEL build for any board with:
make <board>_config
echo CONFIG_SPL_FEL=y >> .config
echo CONFIG_SPL_FEL=y >> spl/.config
or better
make <board>_config
sed -i -e 's/\# CONFIG_SPL_FEL is not set/CONFIG_SPL_FEL=y/g' .config spl/.config
which is still one more step than I would like but still preferable IMHO to:

        sed -i -e 's/^CONFIG_SYS_EXTRA_OPTIONS="[^"]*/&,SPL_FEL/g' .config spl/.config

Near the end I've added a patch which adds <BOARD>_felconfig to automate this, not sure how folks will feel about this, so I've deliberately made it last so it can easily be ignored...

I've been using a little hack (below, updated to use felconfig) to MAKEALL to help build test all this.

Since v1:
* Rebased to current u-boot-sunxi#next
* Hans' equivalent of my first patch has been applied to u-boot-sunxi#next, so my patch is dropped
* Toplevel option is now CONFIG_ARCH_SUNXI
* Per-SoC options are now CONFIG_MACH_SUN[45678]I
* Board selection has been pulled out of CONFIG_SYS_EXTRA_OPTIONS into Kconfig, as CONFIG_TARGET_<BOARD>
* The <BOARD>_FEL_defconfig files are now removed

Ian.

My MAKEALL hack, surely not upstreamable ;-)

index 7c16319..3a8d1d0 100755
@@ -660,6 +660,11 @@ build_target() {
        echo "Building ${target} board..."
        ${MAKE} -s ${target}_defconfig >/dev/null
 
+       if [ -n "$SUNXI_FORCE_FEL" ] ; then
+           sed -i -e 's/\# CONFIG_SPL_FEL is not set/CONFIG_SPL_FEL=y/g' \
+               .config spl/.config
+       fi
+
        ${MAKE} ${JOBS} ${CHECK} all \
                >${LOG_DIR}/$target.MAKELOG 2> ${LOG_DIR}/$target.ERR