ASoC: simple-amplifier: Rename drv_event() function

ASoC: simple-amplifier: Rename drv_event() function

The drv_event() is used to handle power events related to the DRV item.

Later, with the support for gpio-audio-amp, this function will be
also used to handle power events related to the PGA item.

Also, more functions will be added in the driver and it is a common
usage to prefix functions based on the driver name.

Rename the drv_event() function to simple_amp_power_event() to follow
common usage and get rid of the 'drv' term.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Link: https://patch.msgid.link/20260513081702.317117-7-herve.codina@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>