ARM: uniphier: update U-Boot file names in workflow

ARM: uniphier: update U-Boot file names in workflow

Since commit ad1ecd2063da ("fdt: Build a U-Boot binary without device
tree") and commit 03c25bcd263a ("fdt: Build an SPL binary without
device tree"), we can use shorter file names for the output images.

The default configuration for UniPhier SoCs enables CONFIG_OF_SEPARATE
and CONFIG_SPL_OF_CONTROL.  In this case, spl/u-boot-spl.bin is the
same as spl/u-boot-spl-dtb.bin.  Likewise, u-boot.img is the same as
as u-boot-dtb.img.  So, this change of the flow has no impact.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>