arm64: use PC-relative reference for secondary_holding_pen_release

Replace the confusing virtual/physical address arithmetic with a simple
PC-relative reference.
Tested-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/kernel/head.S

@@ -564,10 +564,6 @@ ENTRY(__boot_cpu_mode)
 	.popsection
 
 #ifdef CONFIG_SMP
-	.align	3
-1:	.quad	.
-	.quad	secondary_holding_pen_release
-
 	/*
 	 * This provides a "holding pen" for platforms to hold all secondary
 	 * cores are held until we're ready for them to initialise.
@@ -579,10 +575,7 @@ ENTRY(secondary_holding_pen)
 	mrs	x0, mpidr_el1
 	ldr     x1, =MPIDR_HWID_BITMASK
 	and	x0, x0, x1
-	adr	x1, 1b
-	ldp	x2, x3, [x1]
-	sub	x1, x1, x2
-	add	x3, x3, x1
+	adr_l	x3, secondary_holding_pen_release
 pen:	ldr	x4, [x3]
 	cmp	x4, x0
 	b.eq	secondary_startup