acpi.c: ignore _STA for atrtc SystemCMOS address space is exist if CMOS RTC Not Present bit is not set at IAPC_BOOT_ARCH in FADT.

[takawata]

Summary

atrtc driver implements System CMOS address space and check the bit. So enable probe and attach the driver if the device is disabled.

[jhb]

Suggestion on the commit message:

acpi: Ignore _STA and never disable AT RTC devices

atrtc(4) should always install a SystemCMOS address space handler unless
the RTC Not Present bit is not set in IAPC_BOOT_ARCH in the FADT.
The atrtc(4) driver already checks this bit, but _STA can return not-present
even when this bit is clear.