ARM: dts: vt8500: Add L2 cache controller on WM8850/WM8950

ARM: dts: vt8500: Add L2 cache controller on WM8850/WM8950

WonderMedia WM8850/WM8950 uses an ARM PL310 cache controller for its
L2 cache, add it.

The parameters have been deduced from vendor's U-boot environment
variables, which the downstream code uses to initialize the
controller. They set the following register values:

aux = 0x3e440000
prefetch_ctrl = 0x70000007

Their initialization code also unconditionally sets the flags
L2X0_DYNAMIC_CLK_GATING_EN | L2X0_STNDBY_MODE_EN, so encode those too

Signed-off-by: Alexey Charkov <alchark@gmail.com>
Link: https://lore.kernel.org/r/20250515-wmt-dts-updates-v2-5-246937484cc8@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>