powerpc/rtas: unexport 'rtas' symbol

No modular code needs access to the 'rtas' struct, so remove the
symbol export.
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230124140448.45938-2-nathanl@linux.ibm.com

arch/powerpc/kernel/rtas.c

@@ -63,7 +63,6 @@ static inline void do_enter_rtas(unsigned long args)
 struct rtas_t rtas = {
 	.lock = __ARCH_SPIN_LOCK_UNLOCKED
 };
-EXPORT_SYMBOL(rtas);
 
 DEFINE_SPINLOCK(rtas_data_buf_lock);
 EXPORT_SYMBOL(rtas_data_buf_lock);