bl1/aarch64/early_exceptions.S used to be re-used by BL2, BL3-1 and
BL3-2. There was some early SMC handling code in there that was not
required by the other bootloader stages. Therefore this patch
introduces an even simpler exception vector source file for BL2,
BL3-1 and BL3-2.
FixesARM-software/tf-issues#38
Change-Id: I0244b80e9930b0f8035156a0bf91cc3e9a8f995d