Follow Linux Kernel change introduced in
bdb0066 and avoid device/driver model
for DT-based platforms. See the original kernel commit for the rationale.

Also make syscon_base_lookup_by_pdevname() behave the same way as its
kernel counterpart in the case whern "property" argument is NULL.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>