cpufreq: amd-pstate: Fix struct amd_cpudata kernel-doc comment

Add the description of @req and @boost_supported in struct amd_cpudata
kernel-doc comment to remove warnings found by running scripts/kernel-doc,
which is caused by using 'make W=1'.

drivers/cpufreq/amd-pstate.c:104: warning: Function parameter or member
'req' not described in 'amd_cpudata'
drivers/cpufreq/amd-pstate.c:104: warning: Function parameter or member
'boost_supported' not described in 'amd_cpudata'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>