RISC-V: kconfig cleanups

These three kconfig cleanups were found by ulfalyzer.  They're all
things we were selecting that were undefined, either because they'd been
remove upstream or are part of a future RISC-V submission.

* ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE is obselete.
* RISCV_IRQ_INTC is the old name for our interrupt controller driver,
  it'll be changed for the final submission and doesn't exist now.
* ARCH_WANT_OPTIONAL_GPIOLIB is obselete.

arch/riscv/Kconfig

@@ -8,7 +8,6 @@ config RISCV
 	select OF
 	select OF_EARLY_FLATTREE
 	select OF_IRQ
-	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select ARCH_WANT_FRAME_POINTERS
 	select CLONE_BACKWARDS
 	select COMMON_CLK
@@ -20,7 +19,6 @@ config RISCV
 	select GENERIC_STRNLEN_USER
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_ATOMIC64 if !64BIT || !RISCV_ISA_A
-	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select HAVE_MEMBLOCK
 	select HAVE_MEMBLOCK_NODE_MAP
 	select HAVE_DMA_API_DEBUG
@@ -34,7 +32,6 @@ config RISCV
 	select HAVE_ARCH_TRACEHOOK
 	select MODULES_USE_ELF_RELA if MODULES
 	select THREAD_INFO_IN_TASK
-	select RISCV_IRQ_INTC
 	select RISCV_TIMER
 
 config MMU