target/avr: Add missing includes of qemu/error-report.h

This had been pulled in from tcg/tcg.h, via exec/cpu_ldst.h,
via exec/exec-all.h, but the include of tcg.h will be removed.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>