RISC-V: Refactor the or pattern to switch cases

RISC-V: Refactor the or pattern to switch cases

This patch refactor the pattern A or B or C or D, to the switch case for
easy add/remove new types, as well as human reading friendly.

Before this patch:
return A || B || C || D;

After this patch:
switch (type)
  {
    case A:
    case B:
    case C:
    case D:
      return true;
    default:
      return false;
  }

Signed-off-by: Pan Li <pan2.li@intel.com>
gcc/ChangeLog:

	* config/riscv/riscv-vector-builtins.cc (required_extensions_p):
	Refactor the or pattern to switch cases.