The PLL146x is used to implement SYS_PLL3 on i.MX8MP and can be used
to drive UARTn_ROOT clock. By setting the PLL3 to 320 MHz or 640 MHz,
the PLL3 output can be divided down to supply UARTn_ROOT clock with
precise 64 MHz, which divided down further by 16x oversampling factor
used by the i.MX UART core yields 4 Mbdps baud base for the UART IP.
This is useful e.g. for BCM bluetooth chips, which can operate up to
4 Mbdps.

Add 320 MHz and 640 MHz entries so the PLL can be configured accordingly.
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Link: https://lore.kernel.org/r/20221031204838.195292-1-marex@denx.de