feat(dsu): support power control and autonomous powerdown config

This patch allows platforms to enable certain DSU settings
to ensure memory retention and control over
cache power requests. We also move the driver out of css
into drivers/arm. Platforms can configure the
CLUSTERPWRCTLR and CLUSTERPWRDN registers [1] to improve
power efficiency.

These registers enable finer-grained control of
DSU power state transitions, including
powerdown and retention.

IMP_CLUSTERPWRCTLR_EL1 provides:
- Functional retention: Allows configuration of the
  duration of inactivity before the DSU uses
  CLUSTERPACTIVE to request functional retention.

- Cache power request: These bits are output on
  CLUSTERPACTIVE[19:16] to indicate to the power controller
  which cache portions must remain powered.

IMP_CLUSTERPWRDN_EL1 includes:
- Powerdown: Triggers full cluster powerdown, including
  control logic.

- Memory retention: Requests memory retention mode,
  keeping L3 RAM contents while powering off
  the rest of the DSU.

The DSU-120 TRM [2] provides the full field definitions,
which are used as references in the `dsu_driver_data` structure.

References:
[1]: https://developer.arm.com/documentation/100453/latest/
[2]: https://developer.arm.com/documentation/102547/0201/?lang=en

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: I2eba808b8f2a27797782a333c65dd092b03208fe
diff --git a/plat/arm/css/common/css_pm.c b/plat/arm/css/common/css_pm.c
index 18882d3..80da3d9 100644
--- a/plat/arm/css/common/css_pm.c
+++ b/plat/arm/css/common/css_pm.c
@@ -12,7 +12,7 @@
 #include <bl31/interrupt_mgmt.h>
 #include <common/debug.h>
 #include <drivers/arm/css/css_scp.h>
-#include <drivers/arm/css/dsu.h>
+#include <drivers/arm/dsu.h>
 #include <lib/cassert.h>
 #include <plat/arm/common/plat_arm.h>