storageproxyd: Added support for getting max size of file

This handles the STORAGE_FILE_GET_MAX_SIZE. The new behavior will
return a max size of 0x10000000000 (former default value in Trusty)
for a regular file and the partition size for a block device.

Test: N/A
Bug: 247003431
Change-Id: Ib8b8504b63496d64487cf2f96a1c0758bfafdd97
Signed-off-by: Jay Monkman <jtmjtmjtmjtmjtmjtmjtm@gmail.com>