powerpc: use CONFIG_IS_ENABLED() when checking for DM_SERIAL in include/asm/config.h

Use the CONFIG_IS_ENABLED() macro when checking for DM_SERIAL so that
CFG_SYS_NS16550_CLK is not defined as get_serial_clock() in SPL if SPL
does not have DM_SERIAL enabled.

Signed-off-by: Marek Mojík <marek.mojik@nic.cz>
Reviewed-by: Marek Behún <kabel@kernel.org>
1 file changed