ARM: 6749/1: fold lookup_machine_type() into setup_machine()

Since commit 6fc31d54

 there is no callers for lookup_machine_type()
other than setup_machine(). And if the former fails it won't return,
therefore the error path in the later is dead code.  Let's clean
things up by merging them together.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>