riscv: translate virtual address to physical address. (#425)

* riscv: translate virtual address to physical address.

* riscv: fix formatting errors.

* riscv: fix build errors.

* riscv: Remove redundant command for virtual address access.

* Revert "riscv: Remove redundant command for virtual address access."

This reverts commit 990d09eac37d2effcfc5c0d0b5c99678f45e7d7f.

* riscv: Change command disable_virt2phys  to set_enable_virt2phys

1. Avoid double negative logic to make users easy to use.
2. Add document about new comomand 'riscv set_enable_virt2phys on|off'

doc/openocd.texi

@@ -9472,12 +9472,18 @@ When on, prefer to use System Bus Access to access memory.  When off, prefer to
 use the Program Buffer to access memory.
 @end deffn
 
-@deffn Command {riscv riscv_enable_virtual} on|off
+@deffn Command {riscv set_enable_virtual} on|off
 When on, memory accesses are performed on physical or virtual memory depending
 on the current system configuration. When off, all memory accessses are performed
 on physical memory.
 @end deffn
 
+@deffn Command {riscv set_enable_virt2phys} on|off
+When on, memory accesses are performed on physical or virtual memory depending
+on the current satp configuration. When off, all memory accessses are performed
+on physical memory.
+@end deffn
+
 @deffn Command {riscv resume_order} normal|reversed
 Some software assumes all harts are executing nearly continuously. Such
 software may be sensitive to the order that harts are resumed in. On harts