Add K66F default sd storage

[maclobdell]

Description

K66F has an SD Card. Let's implement it as the default storage using the new default storage mechanism in 5.10. This helps ensure new example apps that use BlockDevice::get_default_instance(); work with no extra configuring.

Pull request type

[ ] Fix
[ ] Refactor
[X] Target update
[ ] Functionality change
[ ] Breaking change

[mmahadevan108]

Will this be using the SD card available via the Arduino connector (e.g ci-test shield)?

[maclobdell]

@mmahadevan108 the K66F has an on-board micro SD card connector. so arduino shield is not necessary.

[maclobdell]

I updated the branch to remove the Feature: Storage, so the CFStore will not be added with this PR.

[yossi2le]

LGTM

[NirSonnenschein]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3418
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8348/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3042
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8348/

[mbed-ci]

Test : SUCCESS

Build number : 3212
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8348/3212