SAM: Fix AT91 USART and add better emulation of LE nodeboards #1291

Job	Run time
Version	5s
Build libpinmame-win-x64	1m 46s
Build libpinmame-win-x86	1m 24s
Build libpinmame-win-arm64	1m 16s
Build libpinmame-osx-x64	2m 12s
Build libpinmame-osx-arm64	1m 44s
Build libpinmame-ios-arm64	1m 4s
Build libpinmame-tvos-arm64	1m 4s
Build libpinmame-linux-x64	3m 1s
Build libpinmame-android-arm64-v8a	1m 24s
Build libpinmame-osx	9s
dispatch	0s
	15m 9s

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