powerpc: Remove flush_instruction_cache() on 8xx

flush_instruction_cache() is never used on 8xx, remove it.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/245cabd8f291facac8c8c5fd370e361a69e02860.1597384145.git.christophe.leroy@csgroup.eu

arch/powerpc/mm/nohash/8xx.c

@@ -244,13 +244,6 @@ void set_context(unsigned long id, pgd_t *pgd)
 	mb();
 }
 
-void flush_instruction_cache(void)
-{
-	isync();
-	mtspr(SPRN_IC_CST, IDC_INVALL);
-	isync();
-}
-
 #ifdef CONFIG_PPC_KUEP
 void __init setup_kuep(bool disabled)
 {