xiaomi-riva: Add initial support for Redmi 5A

I have created new packages for Xiaomi Redmi 5A (riva), the packages are created from the xiami-rolex packages. What's working?

• Display (partial): x11 is working.
• Wifi: It uses rolex's firmwares.
• Audio: broken
• Touchscreen: works

I have found working and partial working lk2nd variants for it.

• https://github.com/msm8953-mainline/lk2nd - It doesn't support riva officially. But with a new dts it can be started on the device. It cannot boot the device.
• https://github.com/mi-msm8937/lk2nd - It supports the device, i can start it but it cannot boot the device. (I should fix the dts/rules.mk)
• https://github.com/geckyn/lk2nd - With a minimal device dts it can start and boot the device but it is old lk2nd variant.

Maybe in the future it can be used with mainline kernel:

• https://github.com/MrArtemSid/linux-msm89x7 xiaomi-rolex already supported but i have issues with booting on a Redmi 3s which is also supported.
• https://github.com/Lanik123/linux it is newer than linux-msm89x7 (iommu support is WIP) xiaomi-rolex already supported but i have issues with booting on a Redmi 3s which is also supported.