i386: Check vector length for scatter/gather prefetch instructions

i386: Check vector length for scatter/gather prefetch instructions

Since not all vector lengths are supported by scatter/gather prefetch
instructions, decode them only with supported vector lengths.

gas/

	PR binutils/24719
	* testsuite/gas/i386/disassem.s: Add test for vgatherpf0dps
	with invalid vector length.
	* testsuite/gas/i386/x86-64-disassem.s: Likewise.
	* testsuite/gas/i386/disassem.d: Updated.
	* testsuite/gas/i386/x86-64-disassem.d: Likewise.

opcodes/

	PR binutils/24719
	* i386-dis-evex-len.h: Add EVEX_LEN_0F38C6_REG_1_PREFIX_2,
	EVEX_LEN_0F38C6_REG_2_PREFIX_2, EVEX_LEN_0F38C6_REG_5_PREFIX_2,
	EVEX_LEN_0F38C6_REG_6_PREFIX_2, EVEX_LEN_0F38C7_R_1_P_2_W_0,
	EVEX_LEN_0F38C7_R_1_P_2_W_1, EVEX_LEN_0F38C7_R_2_P_2_W_0,
	EVEX_LEN_0F38C7_R_2_P_2_W_1, EVEX_LEN_0F38C7_R_5_P_2_W_0,
	EVEX_LEN_0F38C7_R_5_P_2_W_1, EVEX_LEN_0F38C7_R_6_P_2_W_0 and
	EVEX_LEN_0F38C7_R_6_P_2_W_1.
	* i386-dis-evex-prefix.h: Update PREFIX_EVEX_0F38C6_REG_1,
	PREFIX_EVEX_0F38C6_REG_2, PREFIX_EVEX_0F38C6_REG_5 and
	PREFIX_EVEX_0F38C6_REG_6 entries.
	* i386-dis-evex-w.h: Update EVEX_W_0F38C7_R_1_P_2,
	EVEX_W_0F38C7_R_2_P_2, EVEX_W_0F38C7_R_5_P_2 and
	EVEX_W_0F38C7_R_6_P_2 entries.
	* i386-dis.c: Add EVEX_LEN_0F38C6_REG_1_PREFIX_2,
	EVEX_LEN_0F38C6_REG_2_PREFIX_2, EVEX_LEN_0F38C6_REG_5_PREFIX_2,
	EVEX_LEN_0F38C6_REG_6_PREFIX_2, EVEX_LEN_0F38C7_R_1_P_2_W_0,
	EVEX_LEN_0F38C7_R_1_P_2_W_1, EVEX_LEN_0F38C7_R_2_P_2_W_0,
	EVEX_LEN_0F38C7_R_2_P_2_W_1, EVEX_LEN_0F38C7_R_5_P_2_W_0,
	EVEX_LEN_0F38C7_R_5_P_2_W_1, EVEX_LEN_0F38C7_R_6_P_2_W_0 and
	EVEX_LEN_0F38C7_R_6_P_2_W_1 enums.