Enabling AHCI for SSD under Win7 BootCamp on Macbook Pro 2011
You can't.  Apple has implemented a Compatibility Support Module (CSM) into the Mac firmware that emulates the PC BIOS specification.  Since the Mac firmware is not 100% UEFI compliant, that CSM is the only way Windows can boot on a Mac.

Unfortunately, the ACPI tables in that CSM are just the bare minimum necessary to allow Windows to boot and nothing more. You lose several features when using it:


No graphics switching (always uses the discrete card).
No AHCI support (SATA devices are in IDE compatibility mode)

No support for TRIM
No support for Native Command Queuing (NCQ).

No support for advanced power management features (only basic S1, S3, and S4 states are supported).


Basically Windows sees your SSD as just a really fast IDE hard drive.  This will not affect the SSD in terms of lifespan.  It may, however, make the SSD a little slower over time than it would otherwise be when running Windows.

NOTE:  Some people have reported that they have been able to install Windows 7 in UEFI mode on a Mac, which would enable all those missing features.  However, it cannot be done on your model.  I've tried.  With sufficient hacking you can get it up and running, but it's plagued with audio and video issues.