linux-user: Drop unneeded includes from qemu.h

linux-user: Drop unneeded includes from qemu.h

Trim down the #includes in qemu.h where we can, either by
dropping unneeded headers or by moving them to user-internals.h.

This includes deleting a couple of #includes that appear at
weird points midway through the header file.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210908154405.15417-10-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>