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/bl31/bl31.ld.S b/bl31/bl31.ld.S
index e572f9b..dc6e7a4 100644
--- a/bl31/bl31.ld.S
+++ b/bl31/bl31.ld.S
@@ -94,7 +94,7 @@
     } >RAM
 
 #ifdef BL31_PROGBITS_LIMIT
-    ASSERT(. <= BL31_PROGBITS_LIMIT, "BL3-1 progbits has exceeded its limit.")
+    ASSERT(. <= BL31_PROGBITS_LIMIT, "BL31 progbits has exceeded its limit.")
 #endif
 
     stacks (NOLOAD) : {
@@ -184,5 +184,5 @@
         __COHERENT_RAM_END_UNALIGNED__ - __COHERENT_RAM_START__;
 #endif
 
-    ASSERT(. <= BL31_LIMIT, "BL3-1 image has exceeded its limit.")
+    ASSERT(. <= BL31_LIMIT, "BL31 image has exceeded its limit.")
 }