omap2plus-cpufreq: set transition latency to 30ms

Vishwanath says 30ms is best, so I'm gonna agree with him:
http://www.mail-archive.com/linaro-dev@lists.linaro.org/msg01373.html
omap44xx: cpuidle: Update target residencies to saner values

The current values are insane.

There is no possible way power saving
can be attained by heading into C4 for not much more than 1ms. The average
values are in the 20ms range, so why do we need to even entertain entering
at much lower values when we will use more power than we save in doing so.

The actual recommended values are shown in 79e796f7b993bd82ad108fa488c35ddd1b9387eb
but for some obscure reason, in 16385c726d55f9e84bbc60ff9e329a84d56a13a3 and
22e2193661b6bffcfdc1a4d17f6af0d1782ba860 they were updated to match the exit_latency.

This seems horribly wrong to me as there comes a point when the target residency is
so low that you use more power actually entering the state than you gain from the
insignificant amount of time you spend there.

With the values in this commit, C4 state is used for >95% of the time when the screen
is off, with C3 picking up the remainder.
During audio playback, C4 is used ~50% of the time, C3 is used ~25% of the time and C2
picks up whatever is left.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Add C4 state again since TI guys added it to omapzoom - big props to Ezekeel that discovered this patch before and TI used it on their own official tree.
Increase default read ahead buffer to 256KB
Asynchronous I/O latency to a solid-state disk greatly increased
between the 2.6.32 and 3.0 kernels. By removing the plug from
do_io_submit(), we observed a 34% improvement in the I/O latency.

Unfortunately, at this level, we don't know if the request is to
a rotating disk or not.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: linux-aio@kvack.org
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>