regulator: sy8824x: add SY20276 support

The differences between SY8824C and SY20276 are different vsel_min,
vsel_step, vsel_count and regs for mode/enable.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20190827163721.1947f7a0@xhacker.debian


Signed-off-by: Mark Brown <broonie@kernel.org>