elf.h: add NT_RISCV_CSR and NT_RISCV_VECTOR constants

See Linux commit 9300f00439743c4a34d735e1a27118eb68a1504e ("RISC-V: Add
ptrace support for vectors").

include/elf.h

@@ -703,6 +703,8 @@ typedef struct {
 #define NT_MIPS_DSP	0x800
 #define NT_MIPS_FP_MODE	0x801
 #define NT_MIPS_MSA	0x802
+#define NT_RISCV_CSR	0x900
+#define NT_RISCV_VECTOR	0x901
 #define NT_VERSION	1