x86/percpu: Make CONFIG_USE_X86_SEG_SUPPORT work with sparse

x86/percpu: Make CONFIG_USE_X86_SEG_SUPPORT work with sparse

Now that sparse builds enforce the usage of typeof_unqual() the casts in
__raw_cpu_read/write() cause sparse to emit tons of false postive
warnings:

 warning: cast removes address space '__percpu' of expression

Address this by annotating the casts with __force.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/87v7gz0yjv.ffs@tglx
Closes: https://lore.kernel.org/oe-kbuild-all/202601181733.YZOf9XU3-lkp@intel.com/