lib/coreboot_table: Simplify API to set up lb_serial

Instead of having callbacks into serial console code to set up the
coreboot table have the coreboot table code call IP specific code to get
serial information. This makes it easier to reuse the information as the
return value can be used in a different context (e.g. when filling in a
FDT).

This also removes boilerplate code to set up lb_console entries by
setting entry based on the type in struct lb_uart.

Change-Id: I6c08a88fb5fc035eb28d0becf19471c709c8043d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68768
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>

src/include/boot/coreboot_tables.h

@@ -19,8 +19,7 @@ void fill_lb_gpios(struct lb_gpios *gpios);
 void lb_add_gpios(struct lb_gpios *gpios, const struct lb_gpio *gpio_table,
 		  size_t count);
 
-void uart_fill_lb(void *data);
-void lb_add_serial(struct lb_serial *serial, void *data);
+enum cb_err fill_lb_serial(struct lb_serial *serial);
 void lb_add_console(uint16_t consoletype, void *data);
 
 enum cb_err lb_fill_pcie(struct lb_pcie *pcie);