osd/scheduler/mClockScheduler: simplify profile handling

osd/scheduler/mClockScheduler: simplify profile handling

Previously, setting default configs from the configured profile was
split across:
- enable_mclock_profile_settings
- set_mclock_profile - sets mclock_profile class member
- set_*_allocations - updates client_allocs class member
- set_profile_config - sets profile based on client_allocs class member

This made tracing the effect of changing the profile pretty challenging
due passing state through class member variables.

Instead, define a simple profile_t with three constexpr values
corresponding to the three profiles and handle it all in a single
set_config_defaults_from_profile() method.

Signed-off-by: Samuel Just <sjust@redhat.com>