add Spinel SPI interface support

This commit enables the Thread Network HAL to support the Spinel
SPI interface.

Bug: 277286756
Test: Build and run otbr-agent on the emulator.
(cherry picked from https://android-review.googlesource.com/q/commit:7ae6d6f4ffe49c358978b9ea9c670ee2aefe4a27)
Merged-In: I6726eead5686f0afb33e5e2035ebc9021eca5afa
Change-Id: I6726eead5686f0afb33e5e2035ebc9021eca5afa