of: drop symbols declared by _OF_DECLARE() from modules

The users of this macro (OF_EARLYCON_DECLARE, CLK_OF_DECLARE,
IRQCHIP_DECLARE, etc.) are only parsed in the early boot stage.
Such symbols contained in modules are never used.

This commit fixes the link error introduced by commit b8d20e06
("serial: 8250_uniphier: add earlycon support"); the combination
of CONFIG_SERIAL_8250_UNIPHIER=m and CONFIG_SERIAL_8250_CONSOLE=y
fails to link:

ERROR: "early_serial8250_setup" [drivers/tty/serial/8250/8250_uniphier.ko] undefined!

Fixes: b8d20e06 ("serial: 8250_uniphier: add earlycon support")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rob Herring <robh@kernel.org>