coresight: Consolidate clock enabling

CoreSight drivers enable pclk and atclk conditionally. For example,
pclk is only enabled in the static probe, while atclk is an optional
clock that it is enabled for both dynamic and static probes, if it is
present. In the current CoreSight drivers, these two clocks are
initialized separately.  This causes complex and duplicate codes.

CoreSight drivers are refined so that clocks are initialized in one go.
For this purpose, this commit renames coresight_get_enable_apb_pclk() to
coresight_get_enable_clocks() and encapsulates clock initialization
logic:

 - If a clock is initialized successfully, its clock pointer is assigned
   to the double pointer passed as an argument.
 - For ACPI devices, clocks are controlled by firmware, directly bail
   out.
 - Skip enabling pclk for an AMBA device.
 - If atclk is not found, the corresponding double pointer is set to
   NULL. The function returns Success (0) to guide callers can proceed
   with no error.
 - Otherwise, an error number is returned for failures.

The function became complex, move it from the header to the CoreSight
core layer and the symbol is exported. Added comments for recording
details.

Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250731-arm_cs_fix_clock_v4-v6-7-1dfe10bb3f6f@arm.com