8250: microchip: Add 4 Mbps support in PCI1XXXX UART

8250: microchip: Add 4 Mbps support in PCI1XXXX UART

The current clock input is set to 62.5 MHz for supporting fractional
divider, which enables generation of an acceptable baud rate from any
frequency. With the current clock input the baud rate range is limited
to 3.9 Mbps. Hence, the current range is extended to support 4 Mbps
with Burst mode operation. Divisor calculation for a given baud rate is
updated as the sampling rate is reduced from 16 to 8 for 4 Mbps.

Signed-off-by: Rengarajan S <rengarajan.s@microchip.com>
Link: https://lore.kernel.org/r/20240125100619.154873-1-rengarajan.s@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>