payloads: change coreboot to lowercase

The word 'coreboot' should always be written in lowercase, even at the
start of a sentence.

Change-Id: I2ec18ca55e0ea672343a951ab81a24a5630f45fd
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20028
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

payloads/libpayload/arch/arm64/main.c

@@ -64,7 +64,7 @@ static void pre_sysinfo_scan_mmu_setup(void)
 	mmu_presysinfo_memory_used(start, end - start);
 
 	/*
-	 * Memory range 2: Coreboot tables
+	 * Memory range 2: coreboot tables
 	 *
 	 * Maximum size is assumed 2 pages in case it crosses the GRANULE_SIZE
 	 * boundary