re-add grub backgrounds and update grub. mitigate missing characters

mitigate missing characters in unifont for border/arrow characters. this saves
space because now it is no longer necessary to add a custom font

the background added has the libreboot logo on it, and it's 10kb in size unlike
the old gnulove background that was hundreds of KB

resources/coreboot/default/patches/0004-apple-macbook21-Set-default-VRAM-to-64MiB-instead-of.patch

@@ -1,23 +0,0 @@
-From d983a2fdd6434792ea03c6c83c0585b0e403cf31 Mon Sep 17 00:00:00 2001
-From: Leah Rowe <leah@retroboot.org>
-Date: Fri, 19 Mar 2021 05:54:58 +0000
-Subject: [PATCH 04/19] apple/macbook21: Set default VRAM to 64MiB instead of
- 8MiB
-
----
- src/mainboard/apple/macbook21/cmos.default | 2 +-
- 1 file changed, 1 insertion(+), 1 deletion(-)
-
-diff --git a/src/mainboard/apple/macbook21/cmos.default b/src/mainboard/apple/macbook21/cmos.default
-index cf1bc4566e..dc0df3b6d6 100644
---- a/src/mainboard/apple/macbook21/cmos.default
-+++ b/src/mainboard/apple/macbook21/cmos.default
-@@ -5,4 +5,4 @@ boot_devices=''
- boot_default=0x40
- cmos_defaults_loaded=Yes
- lpt=Enable
--gfx_uma_size=8M
-+gfx_uma_size=64M
--- 
-2.25.1
-