firmware_class: Introduce the request_firmware_direct API

On devices with low memory, using request_firmware on rather
large firmware images results in a memory usage penalty that
might be unaffordable. Introduce a new API that allows the
firmware image to be directly loaded to a destination address
without using any intermediate buffer.

Change-Id: I51b55dd9044ea669e2126a3f908028850bf76325
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
[joshc: renamed request_firmware_direct to request_firmware_into_buf,
avoiding namespace conflict]
Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
[vmulukut: upstream merge conflict fixups]
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>