Remove dashes from image names: 'BL3-x' --> 'BL3x'

This patch removes the dash character from the image name, to
follow the image terminology in the Trusted Firmware Wiki page:

    https://github.com/ARM-software/arm-trusted-firmware/wiki

Changes apply to output messages, comments and documentation.

non-ARM platform files have been left unmodified.

Change-Id: Ic2a99be4ed929d52afbeb27ac765ceffce46ed76
diff --git a/common/aarch64/early_exceptions.S b/common/aarch64/early_exceptions.S
index 780a38f..64bfcd0 100644
--- a/common/aarch64/early_exceptions.S
+++ b/common/aarch64/early_exceptions.S
@@ -37,7 +37,7 @@
 
 	/* -----------------------------------------------------
 	 * Very simple stackless exception handlers used by BL2
-	 * and BL3-1 bootloader stages. BL3-1 uses them before
+	 * and BL31 bootloader stages. BL31 uses them before
 	 * stacks are setup. BL2 uses them throughout.
 	 * -----------------------------------------------------
 	 */