gdbstub: Adjust gdb_do_syscall to only use uint32_t and uint64_t

Pass %x as uint32_t and %lx as uint64_t; pass the address
of %s as uint64_t and the length as uint32_t.

Add casts in semihosting/syscalls.c from target_ulong to
uint64_t; add casts from int to uint32_t for clarity.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-28-richard.henderson@linaro.org>