arm64: dts: uniphier: add fixed regulators for audio codec

This patch adds regulators that have fixed voltage for audio codec
on UniPhier LD11/20 Global boards. This patch fixes warnings about
TAS57xx audio codec such as "tas571x 0-001b: 0-001b supply AVDD
not found, using dummy regulator".

Signed-off-by: Katsuhiro Suzuki <suzuki.katsuhiro@socionext.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>