fix(UartStm): use correct registers & fix overrun assert; enable FIFO

[richardapeters]

No description provided.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	5		0	0.02s
✅ MARKDOWN	markdownlint	5	0	0	0.88s
✅ MARKDOWN	markdown-link-check	5		0	4.68s
✅ MARKDOWN	markdown-table-formatter	5	0	0	0.76s
✅ REPOSITORY	checkov	yes		no	19.17s
✅ REPOSITORY	dustilock	yes		no	0.02s
✅ REPOSITORY	gitleaks	yes		no	32.55s
✅ REPOSITORY	git_diff	yes		no	0.46s
✅ REPOSITORY	secretlint	yes		no	12.22s
✅ REPOSITORY	syft	yes		no	1.6s
✅ REPOSITORY	trivy	yes		no	3.66s
✅ SPELL	misspell	28	1	0	0.6s
✅ XML	xmllint	16		0	0.09s
✅ YAML	prettier	7	1	0	1.28s
✅ YAML	v8r	7		0	7.53s
✅ YAML	yamllint	7		0	0.35s

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