drivers/perf: riscv: Disable PERF_SAMPLE_BRANCH_* while not supported

RISC-V perf driver does not yet support branch sampling. Although the
specification is in the works [0], it is best to disable such events
until support is available, otherwise we will get unexpected results.
Due to this reason, two riscv bpf testcases get_branch_snapshot and
perf_branches/perf_branches_hw fail.

Link: https://github.com/riscv/riscv-control-transfer-records

 [0]
Fixes: f5bfa23f ("RISC-V: Add a perf core library for pmu drivers")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240312012053.1178140-1-pulehui@huaweicloud.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>