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been replaced by `ENABLE_ASSERTIONS`.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/aarch32/misc_helpers.S b/lib/aarch32/misc_helpers.S
index 5b17c21..03b47ea 100644
--- a/lib/aarch32/misc_helpers.S
+++ b/lib/aarch32/misc_helpers.S
@@ -162,7 +162,7 @@
  * --------------------------------------------------------------------------
  */
 func memcpy4
-#if ASM_ASSERTION
+#if ENABLE_ASSERTIONS
 	orr	r3, r0, r1
 	tst	r3, #0x3
 	ASM_ASSERT(eq)