serial: Make full device search optional

Commit 608b0c4a ("serial: Use next serial device if probing fails")
added code to search for more serial devices if the default one was not
probed correctly.

Unfortunately, that breaks omap3_evm. So while investigating why that is
the case, let's disable the full search for everyone but bcm283x where it
is needed.

Fixes: 608b0c4a ("serial: Use next serial device if probing fails")
Reported-by: Derald D. Woods <woods.technical@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>