egl-kms: Use drmModePageFlip
egl-kms: Use drmModePageFlip

The KMS platform now uses drmModePageFlip to present the buffer. The
main loop mechanism is used to poll for events on the DRM file
descriptor so that we notice when the page flip is complete. The
swap_buffers is throttled so that if there is a pending flip it will
block until it is complete before starting another flip.

Reviewed-by: Robert Bragg <12e9293ec6b30c7fa8a0926af42807e929c1684f@linux.intel.com>

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