acpi: Rename motherboard_fill_fadt() to mainboard_fill_fadt()

The prefix mainboard_ was used everywhere else.

Change-Id: Ie576fd47301aa484cb1396e0c6f7260b7698af4d
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42007
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/google/rambi/acpi_tables.c

@@ -41,7 +41,7 @@ unsigned long acpi_fill_madt(unsigned long current)
 	return current;
 }
 
-void motherboard_fill_fadt(acpi_fadt_t *fadt)
+void mainboard_fill_fadt(acpi_fadt_t *fadt)
 {
 	fadt->preferred_pm_profile = PM_MOBILE;
 }