riscv: fix build break after macro-to-function conversion in generic cacheflush.h

Commit c296d4dc ("asm-generic: fix a compilation warning")
converted the various flush_*cache_* macros in
asm-generic/cacheflush.h to static inline functions.  This breaks
RISC-V builds, since RISC-V's cacheflush.h includes the generic
cacheflush.h and then undefines the macros to be overridden.

Fix by copying the subset of the no-op functions that are reused from
the generic cacheflush.h into the RISC-V cacheflush.h, and dropping
the include of the generic cacheflush.h.

Fixes: c296d4dc ("asm-generic: fix a compilation warning")
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>

arch/riscv/include/asm/cacheflush.h

@@ -6,11 +6,66 @@
 #ifndef _ASM_RISCV_CACHEFLUSH_H
 #define _ASM_RISCV_CACHEFLUSH_H
 
-#include <asm-generic/cacheflush.h>
+#include <linux/mm.h>
 
-#undef flush_icache_range
-#undef flush_icache_user_range
-#undef flush_dcache_page
+#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
+
+/*
+ * The cache doesn't need to be flushed when TLB entries change when
+ * the cache is mapped to physical memory, not virtual memory
+ */
+static inline void flush_cache_all(void)
+{
+}
+
+static inline void flush_cache_mm(struct mm_struct *mm)
+{
+}
+
+static inline void flush_cache_dup_mm(struct mm_struct *mm)
+{
+}
+
+static inline void flush_cache_range(struct vm_area_struct *vma,
+				     unsigned long start,
+				     unsigned long end)
+{
+}
+
+static inline void flush_cache_page(struct vm_area_struct *vma,
+				    unsigned long vmaddr,
+				    unsigned long pfn)
+{
+}
+
+static inline void flush_dcache_mmap_lock(struct address_space *mapping)
+{
+}
+
+static inline void flush_dcache_mmap_unlock(struct address_space *mapping)
+{
+}
+
+static inline void flush_icache_page(struct vm_area_struct *vma,
+				     struct page *page)
+{
+}
+
+static inline void flush_cache_vmap(unsigned long start, unsigned long end)
+{
+}
+
+static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
+{
+}
+
+#define copy_to_user_page(vma, page, vaddr, dst, src, len) \
+	do { \
+		memcpy(dst, src, len); \
+		flush_icache_user_range(vma, page, vaddr, len); \
+	} while (0)
+#define copy_from_user_page(vma, page, vaddr, dst, src, len) \
+	memcpy(dst, src, len)
 
 static inline void local_flush_icache_all(void)
 {