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been replaced by `ENABLE_ASSERTIONS`.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/include/common/aarch32/el3_common_macros.S b/include/common/aarch32/el3_common_macros.S
index d7e0b3f..9158203 100644
--- a/include/common/aarch32/el3_common_macros.S
+++ b/include/common/aarch32/el3_common_macros.S
@@ -148,7 +148,7 @@
 		_init_memory, _init_c_runtime, _exception_vectors
 
 	/* Make sure we are in Secure Mode */
-#if ASM_ASSERTION
+#if ENABLE_ASSERTIONS
 	ldcopr	r0, SCR
 	tst	r0, #SCR_NS_BIT
 	ASM_ASSERT(eq)