sh: Cleanup about SPARSE_IRQ

After commit 37744fe ("sh: remove sh5 support"), sh always
enable SPARSE_IRQ, kill unused MAY_HAVE_SPARSE_IRQ and NR_IRQS
define.

Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Rich Felker <dalias@libc.org>

arch/sh/Kconfig

@@ -56,7 +56,6 @@ config SUPERH
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_FORCED_THREADING
-	select MAY_HAVE_SPARSE_IRQ
 	select MODULES_USE_ELF_RELA
 	select NEED_SG_DMA_LENGTH
 	select NO_DMA if !MMU && !DMA_COHERENT

arch/sh/include/asm/irq.h

@@ -5,17 +5,6 @@
 #include <linux/cpumask.h>
 #include <asm/machvec.h>
 
-/*
- * Only legacy non-sparseirq platforms have to set a reasonably sane
- * value here. sparseirq platforms allocate their irq_descs on the fly,
- * so will expand automatically based on the number of registered IRQs.
- */
-#ifdef CONFIG_SPARSE_IRQ
-# define NR_IRQS		8
-#else
-# define NR_IRQS		512
-#endif
-
 /*
  * This is a special IRQ number for indicating that no IRQ has been
  * triggered and to simply ignore the IRQ dispatch. This is a special