Integrate meta-seco-imx/u-boot-seco-imx/seco_lf_v2021.04-c26_video

Commit: clea-os/layers/seco/meta-seco-imx@67d8abc7

Integrate u-boot-seco-imx/seco_lf_v2021.04-c26_video

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Commit: clea-os/bsp/nxp/u-boot-seco-imx@2f25747b

[C26][ENV] update video overlay options

• add DP overlay option for CFG=A1
• add DP fw load on overlay option for CFG=A2
• add LVDS ChB 800x480 overlay option
• update multi-video overlay handling: instead of a single unified overlay for every multi-video option use multiple intercompatible video overlay to be used in several combinations

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Commit: clea-os/bsp/nxp/u-boot-seco-imx@d1a1fbee

[C26][C43] remove reference board HDP FW load mechanism

As we use our own method for loading firmwares depending on seco_config tool selected options, reference board mechanism has never been used: remove it.