Tools: Summarize stats when depth is 0

[theotherjimmy]

Description

#5153 describes an odd inconsistency in memap behavior, or at least where
my expectations were let down. It would print the entire memory map at full
depth when the depth was specified as 0. This PR changes that to print
something like:

+-----------+-------+-------+------+
| Module    | .text | .data | .bss |
+-----------+-------+-------+------+
| Subtotals | 38450 |  2564 | 7052 |
+-----------+-------+-------+------+

Resolves #5153

Pull request type

[x] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[cmonr]

Fyi, this still needs to pass Travis.

[theotherjimmy]

Errors reproduced. Fixing.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2526
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7377/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2174
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7377/

[mbed-ci]

Test : SUCCESS

Build number : 2288
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7377/2288