dt-bindings: arm: move cpu-capacity to a shared loation

RISC-V uses the same generic topology code as arm64 & while there
currently exists no binding for cpu-capacity on RISC-V, the code paths
can be hit if the property is present.

Move the documentation of cpu-capacity to a shared location, ahead of
defining a binding for capacity-dmips-mhz on RISC-V. Update some
references to this document in the process.

Signed-off-by: Conor Dooley <[e-mail]>
Reviewed-by: Ley Foon Tan <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Reviewed-by: Yanteng Si <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Palmer Dabbelt <[e-mail]>

Documentation/devicetree/bindings/arm/cpu-capacity.txt Documentation/devicetree/bindings/cpu/cpu-capacity.txt

···
 ==========================================
-ARM CPUs capacity bindings
+CPU capacity bindings
 ==========================================
 
 ==========================================
 1 - Introduction
 ==========================================
 
-ARM systems may be configured to have cpus with different power/performance
+Some systems may be configured to have cpus with different power/performance
 characteristics within the same chip. In this case, additional information has
 to be made available to the kernel for it to be aware of such differences and
 take decisions accordingly.

Documentation/devicetree/bindings/arm/cpus.yaml

···
 
   capacity-dmips-mhz:
     description:
-      u32 value representing CPU capacity (see ./cpu-capacity.txt) in
+      u32 value representing CPU capacity (see ../cpu/cpu-capacity.txt) in
       DMIPS/MHz, relative to highest capacity-dmips-mhz
       in the system.
 

Documentation/scheduler/sched-capacity.rst

···
 
 The arm and arm64 architectures directly map this to the arch_topology driver
 CPU scaling data, which is derived from the capacity-dmips-mhz CPU binding; see
-Documentation/devicetree/bindings/arm/cpu-capacity.txt.
+Documentation/devicetree/bindings/cpu/cpu-capacity.txt.
 
 3.2 Frequency invariance
 ------------------------

Documentation/translations/zh_CN/scheduler/sched-capacity.rst

···
 
 arm和arm64架构直接把这个信息映射到arch_topology驱动的CPU scaling数据中（译注：参考
 arch_topology.h的percpu变量cpu_scale），它是从capacity-dmips-mhz CPU binding中衍生计算
-出来的。参见Documentation/devicetree/bindings/arm/cpu-capacity.txt。
+出来的。参见Documentation/devicetree/bindings/cpu/cpu-capacity.txt。
 
 3.2 频率不变性
 --------------