xscale: better fix for debug_handler.bin

Generate a C struct with the data, and use that, instead of an
assembly language file.  The assembly language causes issues on
Darwin and MS-Windows, which don't necessarily use GNU AS; or
if they do, don't necessarily use its ELF syntax.

It's also better in two other ways:  fewer global symbols; and
the init-time size check gets optimized away at compile time.
(Unless it fails, in which case bigger chunks of the file vanish.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>