drm/amdgpu: add helper function for indirect reg access (v3)

Add helper function in order to remove RREG32/WREG32
in current pcie_rreg/wreg function for soc15 and
onwards adapters.
PCIE_INDEX/DATA pairs are used to access regsiters
outside of mmio bar in the helper functions.
The new helper functions help remove the recursion
of amdgpu_mm_rreg/wreg from pcie_rreg/wreg and
provide the oppotunity to centralize direct and
indirect access in a single function.

v2: Fixed typo and refine the comments

v3: Remove unnecessary volatile local variable

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -1032,6 +1032,19 @@ uint8_t amdgpu_mm_rreg8(struct amdgpu_device *adev, uint32_t offset);
 u32 amdgpu_io_rreg(struct amdgpu_device *adev, u32 reg);
 void amdgpu_io_wreg(struct amdgpu_device *adev, u32 reg, u32 v);
 
+u32 amdgpu_device_indirect_rreg(struct amdgpu_device *adev,
+				u32 pcie_index, u32 pcie_data,
+				u32 reg_addr);
+u64 amdgpu_device_indirect_rreg64(struct amdgpu_device *adev,
+				  u32 pcie_index, u32 pcie_data,
+				  u32 reg_addr);
+void amdgpu_device_indirect_wreg(struct amdgpu_device *adev,
+				 u32 pcie_index, u32 pcie_data,
+				 u32 reg_addr, u32 reg_data);
+void amdgpu_device_indirect_wreg64(struct amdgpu_device *adev,
+				   u32 pcie_index, u32 pcie_data,
+				   u32 reg_addr, u64 reg_data);
+
 bool amdgpu_device_asic_has_dc_support(enum amd_asic_type asic_type);
 bool amdgpu_device_has_dc_support(struct amdgpu_device *adev);