arm_mpam: Check whether the config array is allocated before destroying it

In the Linux kernel, the following vulnerability has been resolved:

arm_mpam: Check whether the config array is allocated before destroying it

__destroy_component_cfg() is called to free the configuration array.

It uses the embedded 'garbage' structure, which means the array has

to be allocated.

If __destroy_component_cfg() is called from mpam_disable() before the

configuration was ever allocated, then a NULL pointer is dereferenced.

Check for this case and return early if the configuration is not

allocated.

__destroy_component_cfg() also frees the mbwu_state as this is allocated

by __allocate_component_cfg(). As the mbwu_state is allocated after

comp->cfg is set, and is also under mpam_list_lock, only the first

pointer needs checking.