When hw.acpi.timer_test_enabled is set to 0, this makes acpi_timer_test return 1
without actually testing the ACPI timer; this results in ACPI-fast being used rather
than potentially using ACPI-safe.
The ACPI timer testing was introduced in 2002 as a workaround for errata in
Pentium II and Pentium III chipsets, and is unlikely to be needed in 2021.
While I'm here, add TSENTER/TSEXIT to make it easier to see the time spent
on the test (if it is enabled).