ACPI: ibm-acpi: extend fan status functions

This patch fixes fan_read to return correct values for all fan access
modes.  It also implements some fan access mode status output that was
missing, and normalizes the proc fan abi to return consistent data across
all fan read/write modes.

Userspace ABI changes and extensions:
	1. Return status: enable/disable for *all* modes
	   (this actually improves compatibility with userspace utils!)
	2. Return level: auto and level: disengaged for EC 2f access mode
	3. Return level: <number> for EC 0x2f access mode
	4. Return level 0 as well as "disabled" in level-aware modes

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>