Reconstruct gaea kernel source for DroidSpaces

[E-R-Butch]

Summary

• replace the unresolved camera, display, and video gitlinks with public same-era SM7250 4.19 sources
• add a minimal Coolpad build skeleton without presenting unavailable private OEM code as recovered source
• restore the public DRM interfaces required by the display techpack
• apply the DroidSpaces non-GKI fixes and enable PID/UTS/IPC namespaces, SysV IPC, device cgroup, devtmpfs, and veth
• retain the public FocalTech/FT3518 implementation and document all source provenance and remaining gaps

Verification

• full ARM64 Image build completed on a case-sensitive Linux volume
• Android Clang r365631c / 9.0.8
• GNU AArch64 ld from Binutils 2.34
• generated Image SHA-256: 57918f5e5c43d436d59bee721f34c52c92fd680c132ceaffa4b1dd405b0a1081
• final config verified with CONFIG_SYSVIPC, CONFIG_POSIX_MQUEUE, CONFIG_PID_NS, CONFIG_UTS_NS, CONFIG_IPC_NS, CONFIG_CGROUP_DEVICE, CONFIG_DEVTMPFS, CONFIG_VETH, and CONFIG_TOUCHSCREEN_FTS built in

Limitations

• not boot-tested on the device yet
• exact private Coolpad drivers and Pixelworks Iris3 4.19 glue remain unavailable and disabled
• proprietary stock boot images, ramdisk, DTB, firmware, and signing material are not committed
• the stock DTB/ramdisk will be used only for a later non-writing temporary boot test after explicit confirmation