fs: add universal exfat driver

this is much more updated and universal than the current exfat driver. furthermore, it should be in fs.

Change-Id: Iee912807399d5aae5ff43d252810c97782251241
Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>
drivers: remove old exfat driver

Change-Id: I94eef7ac6ae9dd3b7e84a31450d1c0a17db085e8
Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>