RISC-V: selftests: Statically link hwprobe test

Statically linking makes it more convenient to copy the test to a
minimal busybox environment.
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230918131518.56803-12-ajones@ventanamicro.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

tools/testing/selftests/riscv/hwprobe/Makefile

@@ -7,4 +7,4 @@ TEST_GEN_PROGS := hwprobe
 include ../../lib.mk
 
 $(OUTPUT)/hwprobe: hwprobe.c sys_hwprobe.S
-	$(CC) -o$@ $(CFLAGS) $(LDFLAGS) $^
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^