linux-user/syscall.c: malloc()/calloc() to g_malloc()/g_try_malloc()/g_new0()

linux-user/syscall.c: malloc()/calloc() to g_malloc()/g_try_malloc()/g_new0()

Convert malloc()/ calloc() calls to g_malloc()/ g_try_malloc()/ g_new0()

All heap memory allocation should go through glib so that we can take
advantage of a single memory allocator and its debugging/tracing features.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Harmandeep Kaur <write.harmandeep@gmail.com>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>