GPU: fix clock frequency detection and overall tidy #550

Job	Run time
MacOS	7m 52s
FreeBSD	8m 58s
Linux	4m 9s
Linux build test (ubuntu-22.04, gcc, g++, ON)	1m 3s
Linux build test (ubuntu-22.04, gcc, g++, OFF)	1m 2s
spellcheck	27s
Win32	9m 2s
Linux build test (ubuntu-22.04, clang, clang++, ON)	1m 13s
Win64	2m 25s
Linux build test (ubuntu-22.04, clang, clang++, OFF)	1m 25s
Linux build test (ubuntu-22.04, musl-gcc, musl-g++, OFF)	57s
Linux build test (ubuntu-20.04, gcc, g++, ON)	1m 23s
Linux build test (ubuntu-20.04, gcc, g++, OFF)	1m 14s
Linux build test (ubuntu-20.04, clang, clang++, ON)	1m 21s
Linux build test (ubuntu-20.04, clang, clang++, OFF)	1m 26s
Linux build test (ubuntu-20.04, musl-gcc, musl-g++, OFF)	1m 3s
Release	0s
	45m 0s

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