regulator: sy8824x: add SY20278 support

The differences between SY8824C and SY20278 are different regs
for mode/enable.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20190827163830.2c94f29b@xhacker.debian


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