uboot-imx

tools: Make kwboot build if HOST_TOOLS_ALL=y

The kwboot tool for Marvell devices isn't currently being built even if
HOST_TOOLS_ALL is set. It doesn't appear to depend on any CONFIG_
options, so it seems appropriate to enable building it here.

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>