riscv: mark some code and data as file-static

Several functions and arrays which are only used in the files in which
they are declared are missing "static" qualifiers.  Warnings for these
symbols are reported by sparse:

arch/riscv/kernel/vdso.c:28:18: warning: symbol 'vdso_data' was not declared. Should it be static?
arch/riscv/mm/sifive_l2_cache.c:145:12: warning: symbol 'sifive_l2_init' was not declared. Should it be static?

Resolve these warnings by marking them as static.

This version incorporates feedback from Greentime Hu
<greentime.hu@sifive.com>.
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Greentime Hu <greentime.hu@sifive.com>

arch/riscv/kernel/vdso.c

@@ -25,7 +25,7 @@ static union {
 	struct vdso_data	data;
 	u8			page[PAGE_SIZE];
 } vdso_data_store __page_aligned_data;
-struct vdso_data *vdso_data = &vdso_data_store.data;
+static struct vdso_data *vdso_data = &vdso_data_store.data;
 
 static int __init vdso_init(void)
 {

arch/riscv/mm/sifive_l2_cache.c

@@ -142,7 +142,7 @@ static irqreturn_t l2_int_handler(int irq, void *device)
 	return IRQ_HANDLED;
 }
 
-int __init sifive_l2_init(void)
+static int __init sifive_l2_init(void)
 {
 	struct device_node *np;
 	struct resource res;