target/hexagon/cpu.h: don't include qemu-common.h

target/hexagon/cpu.h: don't include qemu-common.h

The qemu-common.h header is not supposed to be included from any
other header files, only from .c files (as documented in a comment at
the start of it).

Move the include to linux-user/hexagon/cpu_loop.c, which needs it for
the declaration of cpu_exec_step_atomic().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Message-id: 20211129200510.1233037-3-peter.maydell@linaro.org