target/riscv: add support for svnapot extension

- add PTE_N bit
- add PTE_N bit check for inner PTE
- update address translation to support 64KiB continuous region (napot_bits = 4)

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220204022658.18097-4-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu_bits.h

@@ -561,6 +561,7 @@ typedef enum {
 #define PTE_A               0x040 /* Accessed */
 #define PTE_D               0x080 /* Dirty */
 #define PTE_SOFT            0x300 /* Reserved for Software */
+#define PTE_N               0x8000000000000000ULL /* NAPOT translation */
 
 /* Page table PPN shift amount */
 #define PTE_PPN_SHIFT       10