MIPS: pistachio: Build uImage.gz by default

commit e4f2d1af upstream.

The pistachio platform uses the U-Boot bootloader & generally boots a
kernel in the uImage format. As such it's useful to build one when
building the kernel, but to do so currently requires the user to
manually specify a uImage target on the make command line.

Make uImage.gz the pistachio platform's default build target, so that
the default is to build a kernel image that we can actually boot on a
board such as the MIPS Creator Ci40.

Marked for stable backport as far as v4.1 where pistachio support was
introduced. This is primarily useful for CI systems such as kernelci.org
which will benefit from us building a suitable image which can then be
booted as part of automated testing, extending our test coverage to the
affected stable branches.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
URL: https://groups.io/g/kernelci/message/388


Cc: stable@vger.kernel.org # v4.1+
Cc: linux-mips@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>