Remove build option `ASM_ASSERTION`

The build option `ENABLE_ASSERTIONS` should be used instead. That way
both C and ASM assertions can be enabled or disabled together.

All occurrences of `ASM_ASSERTION` in common code and ARM platforms have
been replaced by `ENABLE_ASSERTIONS`.

ASM_ASSERTION has been removed from the user guide.

Change-Id: I51f1991f11b9b7ff83e787c9a3270c274748ec6f
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/lib/cpus/aarch32/aem_generic.S b/lib/cpus/aarch32/aem_generic.S
index 3d6064c..7374e25 100644
--- a/lib/cpus/aarch32/aem_generic.S
+++ b/lib/cpus/aarch32/aem_generic.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2017, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -35,7 +35,7 @@
 
 func aem_generic_core_pwr_dwn
 	/* Assert if cache is enabled */
-#if ASM_ASSERTION
+#if ENABLE_ASSERTIONS
 	ldcopr	r0, SCTLR
 	tst	r0, #SCTLR_C_BIT
 	ASM_ASSERT(eq)
@@ -51,7 +51,7 @@
 
 func aem_generic_cluster_pwr_dwn
 	/* Assert if cache is enabled */
-#if ASM_ASSERTION
+#if ENABLE_ASSERTIONS
 	ldcopr	r0, SCTLR
 	tst	r0, #SCTLR_C_BIT
 	ASM_ASSERT(eq)