treewide: capitalize 'BIOS'

Also replace 'BIOS' by coreboot when the image is 'coreboot.rom'.

Change-Id: I8303b7baa9671f19a036a59775026ffd63c85273
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38932
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/drivers/intel/gma/int15.c

@@ -33,7 +33,7 @@ int intel_vga_int15_handler(void)
 		 *  bit 2 = Graphics Stretching
 		 *  bit 1 = Text Stretching
 		 *  bit 0 = Centering (do not set with bit1 or bit2)
-		 *  0     = video bios default
+		 *  0     = video BIOS default
 		 */
 		X86_AX = 0x005f;
 		X86_CX = pfit;