riscv: Add HAVE_IRQ_TIME_ACCOUNTING

RISCV_TIMER/CLINT_TIMER is required for RISC-V system, and it
provides sched_clock, which allow us to enable IRQ_TIME_ACCOUNTING.
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Documentation/features/time/irq-time-acct/arch-support.txt

@@ -23,7 +23,7 @@
     |    openrisc: | TODO |
     |      parisc: |  ..  |
     |     powerpc: |  ok  |
-    |       riscv: | TODO |
+    |       riscv: |  ok  |
     |        s390: |  ..  |
     |          sh: | TODO |
     |       sparc: |  ..  |

arch/riscv/Kconfig

@@ -68,6 +68,7 @@ config RISCV
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GCC_PLUGINS
 	select HAVE_GENERIC_VDSO if MMU && 64BIT
+	select HAVE_IRQ_TIME_ACCOUNTING
 	select HAVE_PCI
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS