Setup VBAR_EL3 incrementally

This patch ensures that VBAR_EL3 points to the simple stack-less
'early_exceptions' when the C runtime stack is not correctly setup to
use the more complex 'runtime_exceptions'. It is initialised to
'runtime_exceptions' once this is done.

This patch also moves all exception vectors into a '.vectors' section
and modifies linker scripts to place all such sections together. This
will minimize space wastage from alignment restrictions.

Change-Id: I8c3e596ea3412c8bd582af9e8d622bb1cb2e049d
diff --git a/bl1/bl1.ld.S b/bl1/bl1.ld.S
index 969b8c2..ac52e52 100644
--- a/bl1/bl1.ld.S
+++ b/bl1/bl1.ld.S
@@ -45,6 +45,7 @@
         *bl1_entrypoint.o(.text)
         *(.text)
         *(.rodata*)
+        *(.vectors)
         __RO_END__ = .;
     } >ROM