RISC-V: Access CSRs using CSR numbers

We should prefer accessing CSRs using their CSR numbers because:
1. It compiles fine with older toolchains.
2. We can use latest CSR names in #define macro names of CSR numbers
   as-per RISC-V spec.
3. We can access newly added CSRs even if toolchain does not recognize
   newly addes CSRs by name.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/mm/fault.c

@@ -239,13 +239,9 @@ vmalloc_fault:
 		 * Do _not_ use "tsk->active_mm->pgd" here.
 		 * We might be inside an interrupt in the middle
 		 * of a task switch.
-		 *
-		 * Note: Use the old spbtr name instead of using the current
-		 * satp name to support binutils 2.29 which doesn't know about
-		 * the privileged ISA 1.10 yet.
 		 */
 		index = pgd_index(addr);
-		pgd = (pgd_t *)pfn_to_virt(csr_read(sptbr)) + index;
+		pgd = (pgd_t *)pfn_to_virt(csr_read(CSR_SATP)) + index;
 		pgd_k = init_mm.pgd + index;
 
 		if (!pgd_present(*pgd_k))