Access memory through the scope of current privilege level (#386)

* add opcode for csrrsi and csrrci

* enable MMU while reading/writing memory using progbuf

* fix style issues

* keep old behavior for progbufsize<4, perform r/w/csr only when necessary

* do not pass progbufsize, only write mstatus if changed

* add config option to enable virtualization feature

* throw error if virt enabled but unavaliable, outsource modify_privilege

* support virtualization for read_memory_progbuf_one

doc/openocd.texi

@@ -9491,6 +9491,12 @@ 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
+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 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