staging: zsmalloc: Fix link error on ARM

Testing the arm chromebook config against the upstream
kernel produces a linker error for the zsmalloc module from
staging. The symbol flush_tlb_kernel_range is not available
there. Fix this by removing the reimplementation of
unmap_kernel_range in the zsmalloc module and using the
function directly. The unmap_kernel_range function is not
usable by modules, so also disallow building the driver as a
module for now.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zsmalloc/Kconfig

 config ZSMALLOC
-	tristate "Memory allocator for compressed pages"
+	bool "Memory allocator for compressed pages"
 	default n
 	help
 	  zsmalloc is a slab-based memory allocator designed to store

drivers/staging/zsmalloc/zsmalloc-main.c

@@ -656,11 +656,8 @@ static inline void __zs_unmap_object(struct mapping_area *area,
 				struct page *pages[2], int off, int size)
 {
 	unsigned long addr = (unsigned long)area->vm_addr;
-	unsigned long end = addr + (PAGE_SIZE * 2);
 
-	flush_cache_vunmap(addr, end);
-	unmap_kernel_range_noflush(addr, PAGE_SIZE * 2);
-	flush_tlb_kernel_range(addr, end);
+	unmap_kernel_range(addr, PAGE_SIZE * 2);
 }
 
 #else /* USE_PGTABLE_MAPPING */