linux-user, m68k: select CPU according to ELF header values

linux-user, m68k: select CPU according to ELF header values

M680x0 doesn't support the same set of instructions
as ColdFire, so we can't use "any" CPU type to execute
m68020 instructions.
We select CPU type ("m68040" or "any" for ColdFire)
according to the ELF header. If we can't, we
use by default the value used until now: "any".

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180220173307.25125-4-laurent@vivier.eu>