drm/vc4: Alter the HDMI state machine clock calc to allow for 1920x1200

Whilst the documentation for BCM2835 states that the HDMI state machine
clock needs to be 108% of the pixel clock, other documentation says
that it only has to be greater than the pixel clock. The firmware
uses 101%, and that allows 1920x1200@60Hz to work within the
constraint of the HSM clock being < 163.68MHz.

Adopt 101%, and increase the maximum pixel clock for vc4 to 162MHz
so that it too supports 1920x1200@60.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>