The official support channel for customers who have purchased ARM-supplied development platforms is email:
If in doubt you can contact ARM's general support alias: email@example.com.
You can also ask questions here on Connected Community. Note though that this is a forum for open discussion and comes with no entitlement to support.
Linaro members can also contact Linaro directly for help with relevant issues.
For UEFI support you can either log issues directly or submit questions to one of the public mailing lists:
We recommend custers always use the latest deliverables for their platform, see here. Note that these deliverables target the ARMv8 Foundation Model FVP which is free to download here and is also available as part of ARM DS-5 Development Studio Community Edition.
This means anyone can have a fully functional software stack including ARM Trusted Firmware, UEFI, U-Boot, Linux kernel, and root filesystem, all running on an ARMv8-A model.