riscv: extend execmem_params for generated code allocations

The memory allocations for kprobes and BPF on RISC-V are not placed in
the modules area and these custom allocations are implemented with
overrides of alloc_insn_page() and  bpf_jit_alloc_exec().

Define MODULES_VADDR and MODULES_END as VMALLOC_START and VMALLOC_END for
32 bit and slightly reorder execmem_params initialization to support both
32 and 64 bit variants, define EXECMEM_KPROBES and EXECMEM_BPF ranges in
riscv::execmem_params and drop overrides of alloc_insn_page() and
bpf_jit_alloc_exec().

Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>