serial: s5p: Add Apple M1 support

Apple M1 SoCs include an S5L UART which is a variant of the S5P
UART.  Add support for this variant and enable it by default
on Apple SoCs.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 48188aa..293e3e3 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -924,6 +924,7 @@
 	bool "Apple SoCs"
 	select ARM64
 	select BLK
+	select CLK
 	select CMD_USB
 	select DM
 	select DM_KEYBOARD