dt-bindings: sy8824x: Document SY8824E support

SY8824E is an I2C-controlled adjustable voltage regulator made by
Silergy Corp. The only difference between SY8824C and SY8824E is the
vsel_min.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20190827163505.361890af@xhacker.debian


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