fix copy large file issue over MTP on 32bit device

change offset variable type from off_t to loff_t, then it won't overflow
when the offset value is larger than 2GB.

change the pwrite and pread function to be pwrite64 and pread64 so the
offset parameter won't overflow.

Change-Id: I45947479a59a4240fd708787384bcadee09d8947
Signed-off-by: faqiang.zhu <faqiang.zhu@nxp.com>