cpufreq: CPPC: Add generic helpers for sysfs show/store

cpufreq: CPPC: Add generic helpers for sysfs show/store

Add generic helper functions for u64 sysfs attributes that follow the
common pattern of calling CPPC get/set APIs:
 - cppc_cpufreq_sysfs_show_u64(): reads value and handles -EOPNOTSUPP
 - cppc_cpufreq_sysfs_store_u64(): parses input and calls set function

Add CPPC_CPUFREQ_ATTR_RW_U64() macro to generate show/store functions
using these helpers, reducing boilerplate for simple attributes.

Convert auto_act_window and energy_performance_preference_val to use
the new macro.

No functional changes.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Reviewed-by: Lifeng Zheng <zhenglifeng1@huawei.com>
[ rjw: Retained empty code line after a conditional ]
Link: https://patch.msgid.link/20260120145623.2959636-2-sumitg@nvidia.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>