riscv: tests: Make RISCV_KPROBES_KUNIT tristate

This disallows KUNIT=m and RISCV_KPROBES_KUNIT=y, which produces these
relocs_check.sh warnings when RELOCATABLE=y:

    WARNING: 3 bad relocations
    ffffffff81e24118 R_RISCV_64        kunit_unary_assert_format
    ffffffff81e24a60 R_RISCV_64        kunit_binary_assert_format
    ffffffff81e269d0 R_RISCV_JUMP_SLOT  __kunit_do_failed_assertion

This fixes allmodconfig build.

Reported-by: Inochi Amaoto <inochiama@gmail.com>
Fixes: f2fab61282 ("riscv: Add kprobes KUnit test")
Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
Tested-by: Inochi Amaoto <inochiama@gmail.com>
Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/20251020-riscv-kunit-kconfig-fix-6-18-v1-2-d773b5d5ce48@iscas.ac.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>

arch/riscv/kernel/tests/Kconfig.debug

@@ -31,7 +31,7 @@ config RISCV_MODULE_LINKING_KUNIT
          If unsure, say N.
 
 config RISCV_KPROBES_KUNIT
-       bool "KUnit test for riscv kprobes" if !KUNIT_ALL_TESTS
+       tristate "KUnit test for riscv kprobes" if !KUNIT_ALL_TESTS
        depends on KUNIT
        depends on KPROBES
        default KUNIT_ALL_TESTS

arch/riscv/kernel/tests/kprobes/Makefile

@@ -1 +1,3 @@
-obj-y += test-kprobes.o test-kprobes-asm.o
+obj-$(CONFIG_RISCV_KPROBES_KUNIT) += kprobes_riscv_kunit.o
+
+kprobes_riscv_kunit-objs := test-kprobes.o test-kprobes-asm.o

arch/riscv/kernel/tests/kprobes/test-kprobes.c

@@ -54,3 +54,6 @@ static struct kunit_suite kprobes_test_suite = {
 };
 
 kunit_test_suites(&kprobes_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit test for riscv kprobes");