Support for mbed OS 5.5 / CMSIS v5 RTOS v2

[JanneKiiskila]

Changes required to get the pal to compile with mbed-os-example-client.

This one is on top of PAL R1.0 release (thus can't be merged directly to master).

[JanneKiiskila]

Using the CMSIS-RTOS branch of mbed OS.

https://github.com/ARMmbed/mbed-os/#5fff7e1daeb395aa3d1ecf3f9ec3f4fead3de0c2

Please note that you must update your compiler (GCC to version 6).

Starting mbed Client example
[EasyConnect] IPv4 mode
[EasyConnect] Using Ethernet
[EasyConnect] Connected to Network successfully
[EasyConnect] IP address 192.168.64.86
[EasyConnect] MAC address 5e:44:31:28:c3:5b

SOCKET_MODE : TCP
Connecting to coap://api.connector.mbed.com:5684

Registered object successfully!

[JanneKiiskila]

This one is on top of PAL R1.0 release. There is another PR against PR1.1 as well (#61).

[alekshex]

there seems to be a merge conflict.
why do we need 2 pr's for the same pal master, isn't 61 covers for this one?