HID: intel-ish-hid: Use CPU generation string in driver_data

ISH allows vendors to customize ISH firmware. To differentiate different
vendors and load the correct firmware, Intel defined a firmware file
name format. As part of the filename, there is a "generation" string. To
load correct format the driver must know the generation name to create
file name.

In the absence of any vendor specific firmware, default ISH firmware is
loaded.

Currently full ISH firmware file name is stored as part of driver data.
This file name already includes the generation name. For example, for
Lunar Lake, the name is ish_lnlm.bin, where "lnlm" is the generation.

So instead of storing both generation name and ISH default firmware file
name, just store generation name and create the default ISH firmware
file name string during initialization.

No functional changes are expected.

Signed-off-by: Zhang Lixu <lixu.zhang@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>