x86/boot/compressed/64: Use LEA to initialize boot stack pointer

It's shorter, and it's what is used in every other place, so make it
consistent.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200107194436.2166846-2-nivedita@alum.mit.edu

arch/x86/boot/compressed/head_64.S

@@ -81,9 +81,7 @@ SYM_FUNC_START(startup_32)
 	subl	$1b, %ebp
 
 /* setup a stack and make sure cpu supports long mode. */
-	movl	$boot_stack_end, %eax
-	addl	%ebp, %eax
-	movl	%eax, %esp
+	leal	boot_stack_end(%ebp), %esp
 
 	call	verify_cpu
 	testl	%eax, %eax