Adopt new Ameba SDK source (Preparation for macos compatibility fix)

[chris-hatton]

This PlatformIO integration is not currently macos compatible due to a deficiency of the Realtek SDK itself. This has been raised as an issue against the ambiot/amb1_sdk GitHub repository, where the Ameba SDK is now being maintained.

This PlatformIO integration can prepare to receive this fix and other fixes by adopting the official Amb1 SDK repository as its source for the SDK.

Currently two sources are defined in platform.json:
https://github.com/taubel/sdk-ameba-v4.0b-gcc.git
ssh://git@git.8devices.com/sdk-ameba-v4_0c-gcc.git <- Private, unknown what changes are in 'c'?

Potentially both can be removed and replaced with officially maintained:
https://github.com/ambiot/amb1_sdk

[chris-hatton]

@valinskas Although it's a relatively modest sum; it may still be of interest to you that there's now a $100 USD bounty for having a working PlatformIO / Ameba (RTL8710/8195) integration. It seems that you are very close with this repository and your skill-set; although the SDK is not latest code and has some MacOS compatibility issue which I detailed above.

Also worth mentioning; I started the Ameba SDK upgrade on a fork of your repo but lack the knowledge to complete it successfully in my limited personal time.