riscv: Use kvmalloc_array on relocation_hashtable

riscv: Use kvmalloc_array on relocation_hashtable

The number of relocations may be a huge value that is unallocatable
by kmalloc. Use kvmalloc instead so that it does not fail.

Fixes: 8fd6c5142395 ("riscv: Add remaining module relocations")
Suggested-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Will Pierce <wgpierce17@gmail.com>
Link: https://lore.kernel.org/r/20250402081426.5197-1-wgpierce17@gmail.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>