sam-ba: create $(HOST_DIR)/bin before using it

sam-ba: create $(HOST_DIR)/bin before using it

If one runs "make host-sam-ba" from a clean build, sam-ba.mk cannot
create its symbolic link because $(HOST_DIR)/bin doesn't exist. So
let's create this directory.

>>> host-sam-ba 2.16 Installing to host directory
mkdir -p /buildroot/output/host/opt/sam-ba/
cp -a /buildroot/output/build/host-sam-ba-2.16/* /buildroot/output/host/opt/sam-ba/
ln -sf ../opt/sam-ba/sam-ba_64 /buildroot/output/host/bin/sam-ba
ln: failed to create symbolic link '/buildroot/output/host/bin/sam-ba': No such file or directory
make[1]: *** [package/pkg-generic.mk:234: /buildroot/output/build/host-sam-ba-2.16/.stamp_host_installed] Error 1
make: *** [Makefile:79: _all] Error 2

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>