arm64: dts: imx8mp: Configure VPU clocks for overdrive

The defaults for this SoC are configured for overdrive mode, but
the VPU clocks are currently configured for nominal mode.
Increase VPU_G1_CLK_ROOT to 800MHZ from 600MHz,
Increase VPU_G2_CLK_ROOT to 700MHZ from 500MHz, and
Increase VPU_BUS_CLK_ROOT to 800MHz from 600MHz.

This requires adjusting the clock parents. Since there is already
800MHz clock references, move the VPU_BUS and G1 clocks to it.
This frees up the VPU_PLL to be configured at 700MHz to run
the G2 clock at 700MHz.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>