x86/topology: Add missing struct declaration and attribute dependency

x86/topology: Add missing struct declaration and attribute dependency

The prototypes for get_topology_cpu_type_name() and
get_topology_cpu_type() take a pointer to struct cpuinfo_x86, but
asm/topology.h neither includes nor forward-declares the structure.
Including asm/topology.h, directly or indirectly, without including
asm/processor.h triggers a warning:

    ./arch/x86/include/asm/topology.h:159:47: error: ‘struct cpuinfo_x86’
    declared inside parameter list will not be visible outside of this
    definition or declaration [-Werror]
    159 | const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c);
        |                                               ^~~~~~~~~~~

Since only a pointer is needed, add a forward declaration of struct
cpuinfo_x86.

Additionally, sysctl_sched_itmt_enabled is declared in asm/topology.h with
the __read_mostly attribute, but the header does not include linux/cache.h.
This causes a build failure when including asm/topology.h but not linux/
cache.h:

     ./arch/x86/include/asm/topology.h:264:27: error: expected ‘=’, ‘,’,
     ‘;’, ‘asm’ or ‘__attribute__’ before ‘sysctl_sched_itmt_enabled’
     264 | extern bool __read_mostly sysctl_sched_itmt_enabled;
         |                           ^~~~~~~~~~~~~~~~~~~~~~~~~

Include the required header.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511181954.UMxCeTV1-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511190008.AA0NTn3G-lkp@intel.com/
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Dexuan Cui <dexuan@kernel.org>