Kernel+UE+LibC: Store address as void* in SC_m{re,}map_params

Most other syscalls pass address arguments as `void*` instead of
`uintptr_t`, so let's do that here too. Besides improving consistency,
this commit makes `strace` correctly pretty-print these arguments in
hex.

Kernel/API/Syscall.h

@@ -239,7 +239,7 @@ struct StringListArgument {
 };
 
 struct SC_mmap_params {
-    uintptr_t addr;
+    void* addr;
     size_t size;
     size_t alignment;
     int32_t prot;
@@ -250,7 +250,7 @@ struct SC_mmap_params {
 };
 
 struct SC_mremap_params {
-    uintptr_t old_address;
+    void* old_address;
     size_t old_size;
     size_t new_size;
     int32_t flags;

Kernel/Syscalls/mmap.cpp

@@ -123,7 +123,7 @@ ErrorOr<FlatPtr> Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> use
     REQUIRE_PROMISE(stdio);
     auto params = TRY(copy_typed_from_user(user_params));
 
-    FlatPtr addr = params.addr;
+    auto addr = (FlatPtr)params.addr;
     auto size = params.size;
     auto alignment = params.alignment ? params.alignment : PAGE_SIZE;
     auto prot = params.prot;