flash-arty: Add support for specifying the file type

flash-arty: Add support for specifying the file type

By default openocd tries to "guess" the file type and interpret
it accordingly. For example it will detect an ELF file based on
the presence of an ELF header and will try to load the relevant
segments into the flash.

This may not be what we want. For example, I want to load the raw
ELF file into the flash.

Additionally the ELF parser in most distro's OpenOCD version
only supports ELF32 and will error out.

This adds a "-t" argument to flash-arty to allow us to specify the
file format. For example "-t bin" will treat the file as raw binary.

Unfortunately I had to copy and modify jtagspi.cfg from OpenOCD
to achieve this.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>