ACPI: implement acpi_os_get_timer() according the spec
ACPI Timer() opcode should return monotonically increasing clock with 100ns
granularity according the ACPI 5.0 spec.
Testing the current Timer() implementation with following ASL code (and an
additional debug print in acpi_os_sleep() to get the sleep times dumped out
to dmesg):
The second sleep value is calculated using Timer(). If the implementation
is good enough we should be able to get the second value pretty close to
the first.
However, the current Timer() gives pretty bad sleep times: