riscv: Change type of valid_vm_1_10_[32|64] to bool

riscv: Change type of valid_vm_1_10_[32|64] to bool

This array is actually used as a boolean so swap its current char type
to a boolean and at the same time, change the type of validate_vm to
bool since it returns valid_vm_1_10_[32|64].

Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Message-ID: <20230303131252.892893-3-alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>