refactor(cpus): convert checker functions to standard helpers

The library check_erratum_ls already incorporates the check. The return
of ERRATA_MISSING is handled in the errata_report.c functions.

Change-Id: Ic1dff2bc5235195f7cfce1709cd42467f88b3e4c
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/lib/cpus/aarch64/cortex_a520.S b/lib/cpus/aarch64/cortex_a520.S
index 811c836..d9e654b 100644
--- a/lib/cpus/aarch64/cortex_a520.S
+++ b/lib/cpus/aarch64/cortex_a520.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2025, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -39,20 +39,7 @@
 workaround_runtime_start cortex_a520, ERRATUM(2938996), ERRATA_A520_2938996, CORTEX_A520_MIDR
 workaround_runtime_end cortex_a520, ERRATUM(2938996)
 
-check_erratum_custom_start cortex_a520, ERRATUM(2938996)
-
-       /* This erratum needs to be enabled for r0p0 and r0p1.
-        * Check if revision is less than or equal to r0p1.
-        */
-
-#if ERRATA_A520_2938996
-       mov     x1, #1
-       b       cpu_rev_var_ls
-#else
-       mov     x0, #ERRATA_MISSING
-#endif
-       ret
-check_erratum_custom_end cortex_a520, ERRATUM(2938996)
+check_erratum_ls cortex_a520, ERRATUM(2938996), CPU_REV(0, 1)
 
 	/* ----------------------------------------------------
 	 * HW will do the cache maintenance while powering down
diff --git a/lib/cpus/aarch64/cortex_x4.S b/lib/cpus/aarch64/cortex_x4.S
index 1e81892..4b1cf91 100644
--- a/lib/cpus/aarch64/cortex_x4.S
+++ b/lib/cpus/aarch64/cortex_x4.S
@@ -32,20 +32,7 @@
 workaround_runtime_start cortex_x4, ERRATUM(2726228), ERRATA_X4_2726228, CORTEX_X4_MIDR
 workaround_runtime_end cortex_x4, ERRATUM(2726228)
 
-check_erratum_custom_start cortex_x4, ERRATUM(2726228)
-
-	/* This erratum needs to be enabled for r0p0 and r0p1.
-	 * Check if revision is less than or equal to r0p1.
-	 */
-
-#if ERRATA_X4_2726228
-	mov	x1, #1
-	b	cpu_rev_var_ls
-#else
-	mov	x0, #ERRATA_MISSING
-#endif
-	ret
-check_erratum_custom_end cortex_x4, ERRATUM(2726228)
+check_erratum_ls cortex_x4, ERRATUM(2726228), CPU_REV(0, 1)
 
 /* Disable hardware page aggregation. Enables mitigation for `CVE-2024-5660` */
 workaround_reset_start cortex_x4, CVE(2024, 5660), WORKAROUND_CVE_2024_5660