arm: Use E_FOOmode instead of FOOmode in arm_preferred_simd_mode

arm: Use E_FOOmode instead of FOOmode in arm_preferred_simd_mode

gcc-4.8.5 does not accept case clauses with non-literal type, which
happens for "QImode" as it expands to (scalar_int_mode
((scalar_int_mode::from_int) E_QImode)).

Use E_QImode instead in arm_preferred_simd_mode, to fix the
build. Same for HImode, SImode, HFmode and SFmode as introduced by a
recent patch.

2020-10-12  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* config/arm/arm.c (arm_preferred_simd_mode): Use E_FOOmode
	instead of FOOmode.