ubimkvol: add -m option to create volume of maximum size

Signed-off-by: Paul B. Henson <henson@acm.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ubi_tools: extend supported volume size to 64 bits; shrink code

function                                             old     new   delta
get_num_from_file                                      -      90     +90
packed_usage                                       29395   29377     -18
ubi_tools_main                                      1349    1141    -208
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/2 up/down: 90/-226)          Total: -136 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ubi_tools: add forgotten argv++

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ubi_tools: enhance -s option to allow size multiplier to match mtd-utils

Based on patch by Paul B. Henson <henson@acm.org>

function                                             old     new   delta
static.size_suffixes                                   -      32     +32
ubi_tools_main                                      1141    1148      +7

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>