RISC-V: Don't use a global include guard for uapi/asm/syscalls.

From: Palmer Dabbelt
Date: Thu Aug 09 2018 - 18:34:31 EST


It turns out that we weren't actually hooking sys_riscv_flush_icache
into the syscall table, which results in any flush_icache() call that
escapes the vDSO to silently do nothing.

Changes since v2:

* sys_riscv_flush_icache actually flushes the icache when SMP=n. Thanks
to Andrew for pointing out the I screwed it up!

Changes since v1:

* sys_riscv_flush_icache is now defined even when SMP=n, which allows
this patch set to build against SMP=n and SMP=y.