arch/x86/bootblock.ld: Align the bottom of the bootblock to 64 bytes

Align the bootblock size to 64 bytes because:
- cachelines are often 64 bytes large
- Bootguard/CBnT requires a 64 byte alignment

Change-Id: I69cdacdd15bfca1b91b6f271f2ff76889969fd91
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55046
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/arch/x86/bootblock.ld

@@ -17,7 +17,7 @@ SECTIONS {
 	. = _ebootblock - CONFIG_C_ENV_BOOTBLOCK_SIZE;
 #else
 	. = BOOTBLOCK_TOP - PROGRAM_SZ;
-	. = ALIGN(16);
+	. = ALIGN(64);
 #endif
 
 	_bootblock = .;