Method vmask

Source/astcenc_vecmathlib_rvv_n.h:253–256

* @brief Construct from an existing SIMD register. */

	 * @brief Construct from an existing SIMD register.
	 */
	ASTCENC_SIMD_INLINE explicit vmask(vbool_t a)
	{
		m = a;
	}

	/**
	 * @brief Construct from 1 scalar value.