riscv64: Add gdbserver support

[laokz]

@Xeonacid and me cooperated out these patches. The 1st one add gdbserver support. Main dataset came from most recently GDB source and shadow registers xml also based on them.

The 2nd one fixed some code to let gdbserver_tests passed.

• Add 'ebreak' IR. There is a 'ebreak' instruction after jal __libc_start_main in RISC-V binary . Some tests need vgdb to decode it otherwise would failed.
• Add 'sched_setaffinity' syscall. Test program sleepers.c needs it to work.
• Add gdb output filter for hginfo.vgtest. In gdb 10.3.1, gdb output additional information compared with the expected result.
• Eliminate 'static' of TLS storage in tls.c. It seems that GCC doesn't support DW_OP_GNU_push_tls_address for RISC-V, and always optimized out 'static __thread' variable address. This behavior does not affect program running, but when debug try to acquire its address, Can't take address of "local" which isn't an lvalue.

With these patches, all 25 gdbserver_tests get passed.

[petrpavlu]

Thanks @laokz for working on this. I should get to reviewing the code sometime next week. Apologies for the delay.

[laokz]

All other issues will be fixed on next version. Thanks for your comments.

[laokz]

This version removed filter_helgrind_monitor and tls.c patches. They'll be investigated later. All other issues were fixed.

[petrpavlu]

Thanks!