power: domain: Introduce driver for raw TI K3 PDs

Normally, power domains are handled via TI-SCI in K3 SoCs. However,
SPL is not going to have access to sysfw resources, so it must control
them directly. Add driver for supporting this.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tero Kristo <kristo@kernel.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>