mgmt: mcumgr: Add Kconfig option to manage SMP service registration

Added the CONFIG_MCUMGR_TRANSPORT_BT_DYNAMIC_SVC_REGISTRATION Kconfig
option to manage how the SMP service should be registered.
By default the SMP service must be registered at runtime.
If this Kconfig option is disabled, the SMP service is statically
defined and registered.

This change allows to opt out of using the CONFIG_BT_GATT_DYNAMIC_DB
Kconfig option and as a result, lower the memory usage.

Signed-off-by: Mateusz Kapala <mateusz.kapala@nordicsemi.no>