riscv: Remove ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE select

The ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE symbol was removed in
commit 51a02124 ("atomic64: no need for
CONFIG_ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE").

Remove the ARCH_HAS_ATOMIC64_DEC_IS_POSITIVE select from RISCV.

Discovered with the
https://github.com/ulfalizer/Kconfiglib/blob/master/examples/list_undefined.py
script.
Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

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