arm_mpam: Generate a configuration for min controls

MPAM supports a minimum and maximum control for memory bandwidth. The
purpose of the minimum control is to give priority to tasks that are
below their minimum value. Resctrl only provides one value for the
bandwidth configuration, which is used for the maximum.

The minimum control is always programmed to zero on hardware that
supports it.

Generate a minimum bandwidth value that is 5% lower than the
value provided by resctrl. This means tasks that are not
receiving their target bandwidth can be prioritised by the
hardware.

CC: Zeng Heng <zengheng4@huawei.com>
Signed-off-by: James Morse <james.morse@arm.com>