drm/i915/bxt: Path added of dmc firmware ver1 for BXT.

Broxton also has dmc to manage low-power display engine state.
Path of the firmware added in intel_csr.c.

Naming convention followed as <platform>_dmc_<api-version>.bin

v1: Initial version.

v2: Commit description added based on review comment from Sunil.

Cc: Damien Lespiau <damien.lespiau@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Sunil Kamath <sunil.kamath@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_csr.c

@@ -42,8 +42,10 @@
  */
 
 #define I915_CSR_SKL "i915/skl_dmc_ver1.bin"
+#define I915_CSR_BXT "i915/bxt_dmc_ver1.bin"
 
 MODULE_FIRMWARE(I915_CSR_SKL);
+MODULE_FIRMWARE(I915_CSR_BXT);
 
 /*
 * SKL CSR registers for DC5 and DC6
@@ -409,6 +411,8 @@ void intel_csr_ucode_init(struct drm_device *dev)
 
 	if (IS_SKYLAKE(dev))
 		csr->fw_path = I915_CSR_SKL;
+	else if (IS_BROXTON(dev_priv))
+		csr->fw_path = I915_CSR_BXT;
 	else {
 		DRM_ERROR("Unexpected: no known CSR firmware for platform\n");
 		intel_csr_load_status_set(dev_priv, FW_FAILED);