simplify XScale debug handler installation

Load the XScale debug handler from the read-only data section
instead of from a separate file that can get lost or garbaged.
This eliminates installation and versioning issues, and also
speeds up reset handling a bit.

Plus some minor bits of cleanup related to loading that handler:
comments about just what this handler does, and check fault codes
while writing it into the mini-icache.

The only behavioral changes should be cleaner failure modes after
errors during handler loading, and being a bit faster.

NOTE:  presumes GNU assembly syntax, with ".incbin"; and ELF,
because of the syntax of the ".size" directive.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/xscale.h

@@ -170,4 +170,10 @@ enum
 
 #define ERROR_XSCALE_NO_TRACE_DATA	(-1500)
 
+/* This XScale "debug handler" is loaded into the processor's
+ * mini-ICache, which is 2K of code writable only via JTAG.
+ */
+extern const uint8_t xscale_debug_handler[];
+extern const uint32_t xscale_debug_handler_size;
+
 #endif /* XSCALE_H */