drm/i915/display: replace dig_port->saved_port_bits with flags

dig_port->saved_port_bits is used to permanently store two DDI_BUF_CTL
bits, DDI_BUF_PORT_REVERSAL and DDI_A_4_LANES. Store them separately as
bools to make their use more logical and less about storing state as
register bits.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241129102503.452272-1-jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>