Intel IPU6: Move firmware binaries under ipu/

Move the IPU6 firmware binaries under ipu/ directory. This way it should
be easier to distinguish IPU binaries from the rest in the future.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

WHENCE

@@ -1172,13 +1172,13 @@ Licence: Redistributable. See LICENSE.ipu3_firmware for details
 
 Driver: intel-ipu6-isys - Intel IPU6 (Image Processing Unit 6) driver
 
-File: intel/ipu6epadln_fw.bin
-File: intel/ipu6ep_fw.bin
-File: intel/ipu6epmtl_fw.bin
-File: intel/ipu6_fw.bin
+File: intel/ipu/ipu6epadln_fw.bin
+File: intel/ipu/ipu6ep_fw.bin
+File: intel/ipu/ipu6epmtl_fw.bin
+File: intel/ipu/ipu6_fw.bin
 Version: scci_master_20230926_0007
 
-File: intel/ipu6se_fw.bin
+File: intel/ipu/ipu6se_fw.bin
 Version: scci_master_20210502_1459
 
 Licence: Redistributable. See LICENSE.ivsc for details