SPC Codec: Add ARMv5 optimized code. Easy peasy.

Why? Why not? Cuts a few MHz.

Change-Id: Ied5c70b1aedd255cbe5d42b7d3028bbe47aad01d
buflib: Remove compulsory IRQ disable during buffer move.

It can cause excessively long interrupt outages if moving a larger
buffer and disrupt audio where DMA is not at a higher interrupt priority
such as FIQ.

Some targets, like Gigabeat S, have very low audio interrupt latency
requirements and will even channel swap if they are missed. Pictureflow
will make the issue very obvious. Even then, moves could take
milliseconds or more depending on the buffer size which is far too long
for any target.

Change-Id: I8e7817213e901da67c36b7eb25d7cb1c1e3ba802
Reviewed-on: http://gerrit.rockbox.org/472
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested-by: Michael Sevakis <jethead71@rockbox.org>
Remove dsp_callback because DSP is now library code, not app code.

Yep, nope, not necessary anymore. Just call functions directly.

Change-Id: I21dc35f8d674c2a9c8379b7cebd5613c1f05b5eb
Fix 6e211ab errors and warnings.

If target has HW tone controls but no HW prescaler (non-implemented or
non-existent), audiohw_set_prescaler() should, for now, do nothing.

Change-Id: If1b1a36970dca82fda1c350fbaa4d6ce068a6d32
Fix return address when data_abort_handler skips faulting instruction.

When writing a value to PC, execution continues at that location,
so subtracting 4 returns to the next instruction. Previously, two
instructions after the faulting instruction were being skipped, causing
safe_read functions to return true even if a data abort happened.

Change-Id: I3fd02d54646323ea2050d0504e38f6d22f09c749
Remove data_abort_handler from ARM crt0 files.

This causes data_abort_handler from lib/unwarminder/safe_read.S to be
used instead. It allows unwarminder to avoid data aborts when
displaying the backtrace. A data_abort_handler remains in system-arm.c,
but it is not used because it is declared as a weak symbol.

Change-Id: I832066ed514347fe697e219872e90fbdd937f477
Reviewed-on: http://gerrit.rockbox.org/475
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>
Tested-by: Boris Gjenero <boris.gjenero@gmail.com>
Add DAC's oversampling filter roll-off selection to sound settings.

Change-Id: I1258ba50dd9308f49d97965562f3a423c9bfb785
df1704: Add filter roll-off selection.

Change-Id: I732ebd3446858b497105cf03fc81e934a749a57b