riscv: Enable PM_GENERIC_DOMAINS for T-Head SoCs

T-Head SoCs feature separate power domains (power islands) for major
components like the GPU, Audio, and NPU. To manage the power states of
these components effectively, the kernel requires generic power domain
support.

This commit enables `CONFIG_PM_GENERIC_DOMAINS` for T-Head SoCs,
allowing the power domain driver for these components to be compiled and
integrated. This ensures proper power management and energy efficiency
on T-Head platforms.

By selecting `PM_GENERIC_DOMAINS`, we provide the necessary framework
for the power domain drivers to function correctly on RISC-V
architecture with T-Head SoCs.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Reviewed-by: Drew Fustini <drew@pdp7.com>
Acked-by: Drew Fustini <drew@pdp7.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

arch/riscv/Kconfig.socs

@@ -54,6 +54,7 @@ config ARCH_THEAD
 	bool "T-HEAD RISC-V SoCs"
 	depends on MMU && !XIP_KERNEL
 	select ERRATA_THEAD
+	select PM_GENERIC_DOMAINS if PM
 	help
 	  This enables support for the RISC-V based T-HEAD SoCs.