x86/head/64: Mark 'startup_gdt[]' and 'startup_gdt_descr' as __initdata

As 'startup_gdt[]' and 'startup_gdt_descr' are only used in booting,
mark them as __initdata to allow them to be freed after boot.
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/c85903a7cfad37d14a7e5a4df9fc7119a3669fb3.1689130310.git.houwenlong.hwl@antgroup.com

arch/x86/kernel/head64.c

@@ -69,7 +69,7 @@ EXPORT_SYMBOL(vmemmap_base);
 /*
  * GDT used on the boot CPU before switching to virtual addresses.
  */
-static struct desc_struct startup_gdt[GDT_ENTRIES] = {
+static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
 	[GDT_ENTRY_KERNEL32_CS]         = GDT_ENTRY_INIT(0xc09b, 0, 0xfffff),
 	[GDT_ENTRY_KERNEL_CS]           = GDT_ENTRY_INIT(0xa09b, 0, 0xfffff),
 	[GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(0xc093, 0, 0xfffff),
@@ -79,7 +79,7 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = {
  * Address needs to be set at runtime because it references the startup_gdt
  * while the kernel still uses a direct mapping.
  */
-static struct desc_ptr startup_gdt_descr = {
+static struct desc_ptr startup_gdt_descr __initdata = {
 	.size = sizeof(startup_gdt)-1,
 	.address = 0,
 };