boot/uboot: Call 'make all' unconditionally

boot/uboot: Call 'make all' unconditionally

Since commit fad58cefa4a392b ("boot/uboot: allow to build multiple U-Boot
images") the installation of SPL binary fails.

For example, when building the mx6cubox_defconfig target we see:

  LD      u-boot
  OBJCOPY u-boot-nodtb.bin
  COPY    u-boot.bin
  MKIMAGE u-boot.img
>>> uboot 2016.09.01 Installing to target
>>> uboot 2016.09.01 Installing to images directory
cp -dpf /home/fabio/buildroot/output/build/uboot-2016.09.01/u-boot.bin /home/fabio/buildroot/output/images/
cp -dpf /home/fabio/buildroot/output/build/uboot-2016.09.01/u-boot.img /home/fabio/buildroot/output/images/
cp -dpf /home/fabio/buildroot/output/build/uboot-2016.09.01/SPL /home/fabio/buildroot/output/images/
cp: cannot stat '/home/fabio/buildroot/output/build/uboot-2016.09.01/SPL': No such file or directory

Instead of calling 'make all' only for the BR2_TARGET_UBOOT_FORMAT_DTB_IMG
case, call 'make all' unconditionally so that the SPL target can also
be installed.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>