fix(misra): fix MISRA defects

This patch resolves the MISRA issues reported in mailing list.
It addresses the following MISRA Rules violations - Rule 15.7 and
Rule 2.4.

* As per Rule 15.7, All if.. else if constructs should be terminated
with an else statement and hence the conditional block
has been changed to switch..case. Updated get_el_str() to include
all EL cases.

* As per Rule 2.4, A project should not contain unused tag declarations,
hence intr_type_desc tag is removed.

* bl31_lib_init is only used in translation unit and hence it's
declaration is removed from bl31.h and the definition is made static to
maintain visibility.

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: Ica1d3041566baf51befcad5fd3714189117ba193
diff --git a/bl31/bl31_main.c b/bl31/bl31_main.c
index c8cc2c7..9807817 100644
--- a/bl31/bl31_main.c
+++ b/bl31/bl31_main.c
@@ -83,7 +83,7 @@
 /*******************************************************************************
  * Simple function to initialise all BL31 helper libraries.
  ******************************************************************************/
-void __init bl31_lib_init(void)
+static void __init bl31_lib_init(void)
 {
 	cm_init();
 }