mksyscall need handle 64bit type correctly

up_syscallx supported by arch can only handle the native integer(uintptr_t) correctly. Since uintptr_t on 32bit arch is 32bit, but functions listed below need pass or return 64bit value:

1. clock_t clock(void) when CONFIG_SYSTEM_TIME64==y
2. off_t lseek(int fd, off_t offset, int whence) when CONFIG_FS_LARGEFILE==y

mksyscall need modify in this case by:

1. Proxy split 64bit to two 32bit before invoke sys_call
2. Sub merge two 32bit to 64bit before invoke the real function

See the dissussion here: https://github.com/apache/incubator-nuttx/issues/4206