of: fdt: Honor CONFIG_CMDLINE* even without /chosen node

I do not read a strict requirement on /chosen node in either ePAPR or in
Documentation/devicetree. Help text for CONFIG_CMDLINE and
CONFIG_CMDLINE_EXTEND doesn't make their behavior explicitly dependent on
the presence of /chosen or the presense of /chosen/bootargs.

However the early check for /chosen and bailing out in
early_init_dt_scan_chosen() skips CONFIG_CMDLINE handling which is not
really related to /chosen node or the particular method of passing cmdline
from bootloader.

This leads to counterintuitive combinations (assuming
CONFIG_CMDLINE_EXTEND=y):

a) bootargs="foo", CONFIG_CMDLINE="bar" => cmdline=="foo bar"
b) /chosen missing, CONFIG_CMDLINE="bar" => cmdline==""
c) bootargs="", CONFIG_CMDLINE="bar" => cmdline==" bar"

Move CONFIG_CMDLINE handling outside of early_init_dt_scan_chosen() so that
cases b and c above result in the same cmdline.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/11af73e05bad75e4ef49067515e3214f6d944b3d.camel@gmail.com
Signed-off-by: Rob Herring <robh@kernel.org>