arm64: drop sleep_idmap_phys and clean up cpu_resume()

Two cleanups of the asm function cpu_resume():
- The global variable sleep_idmap_phys always points to idmap_pg_dir,
  so we can just use that value directly in the CPU resume path.
- Unclutter the load of sleep_save_sp::save_ptr_stash_phys.

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/sleep.S

@@ -164,15 +164,12 @@ ENTRY(cpu_resume)
 #else
 	mov	x7, xzr
 #endif
-	adrp	x0, sleep_save_sp
-	add	x0, x0, #:lo12:sleep_save_sp
-	ldr	x0, [x0, #SLEEP_SAVE_SP_PHYS]
+	ldr_l	x0, sleep_save_sp + SLEEP_SAVE_SP_PHYS
 	ldr	x0, [x0, x7, lsl #3]
 	/* load sp from context */
 	ldr	x2, [x0, #CPU_CTX_SP]
-	adrp	x1, sleep_idmap_phys
 	/* load physical address of identity map page table in x1 */
-	ldr	x1, [x1, #:lo12:sleep_idmap_phys]
+	adrp	x1, idmap_pg_dir
 	mov	sp, x2
 	/*
 	 * cpu_do_resume expects x0 to contain context physical address