OMAP: Improve register access in L3 Error handler.

* Changed the way of accessing L3 target
  registers from standard base rather
  than relative to STDERRLOG_MAIN.

* Use ffs() to find error source from
  the L3_FLAGMUX_REGERRn register.

* Remove extra l3_base[] entry.

* Modified L3 custom error message.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: sricharan <r.sricharan@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>