linux-yocto: Modify dtb files path for ARM 3.10

- When compiling ARM 3.10 kernels, the dtb files are created in a
different path. Adapt this path to found the dtb files.
- Do not create fit image for axm55xxemu7 because the dts was
deleted. The version of emulation that used this device tree is
no longer supported.

Signed-off-by: Daniel Dragomir <daniel.dragomir@windriver.com>