Bluetooth: ISO: Speed up BT ISO data processing

For the native posix build the sleep calls used in tasks will stall
the zephyr instance which sets an upper limit on the data processing
interval to once every 20-30 millisecond.
This change reduces the duration of the sleep calls and increases the
TICKS_PER_SECOND to allow for shorter sleeps. This is needed to
support the data rates needed for LE Audio streaming. The rate is
tuned to support up to bidirectional 5ms ISO-intervals.
This change also increases the ISO buffer count from 1 to 5 to
allow for some buffering in the controller, which is needed for
gapless playback and/or use of burst number larger than 1.

Signed-off-by: Casper Bonde <casper_bonde@bose.com>