wb_slave: add config register

With this in place, software can probe the number of voices
and wavetable size automatically.
sw: initialize timer
sw/sublime: fix one-off in MAX_NUM_VOICES
sw/sublime: fix bug in voice reset

Sublime base is already added in sublime_write_reg,
adding it in the function call is wrong.
sw/sublime: remove local SUBLIME_BASE define

Instead, feed the init function with the base address and hold
that in the sublime struct.
Also, use the config register to obtain the number of voices
instead of passing it to the init function.
sw: add envelope implementation
sw/sublime: remove debug printf's
sw/sublime: add amplitude envelope