bootman/update: Only use the system vtable ops
bootman/update: Only use the system vtable ops

To allow further mocking, we ensure we proxy the mount family calls through
the system vtable, allowing us to overide it at a future date to be safe.

Signed-off-by: Ikey Doherty <15e2f59c60e9d84348e78a87e24660774f739add@intel.com>

ikeydoherty/clr-boot-manager,ikeydoherty/clr-boot-manager,ikeydoherty/clr-boot-manager,ikeydoherty/clr-boot-manager