Cellular: Fix Greentea cellular power test

[AriParkkila]

Description

Fixed Greentea cellular power test, that was missing some include headers.

Arm internal ref IOTCELL-1417.

Pull request type

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

[AriParkkila]

@jarvte please review

[AnttiKauppila]

@0xc0170 Can you trigger a build for this?

[NirSonnenschein]

/morph build

[mbed-ci]

Build : FAILURE

Build number : 3269
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8236/

[NirSonnenschein]

@AriParkkila there seems to be a build issue (probably just a configuration issue):
[Error] main.cpp@27,0: #35: #error directive: [NOT_SUPPORTED] CELLULAR_DEVICE must be defined
[DEBUG] Return: 1
[DEBUG] Output: "./features/cellular/TESTS/api/cellular_information/main.cpp", line 27: Error: #35: #error directive: [NOT_SUPPORTED] CELLULAR_DEVICE must be defined
[DEBUG] Output: ./features/cellular/TESTS/api/cellular_information/main.cpp: 0 warnings, 1 error
Building project udp (K64F, ARM)
Please take a look

[AriParkkila]

We have excluded tests from Greentea by #error [NOT_SUPPORTED] Something more must be defined to run this test case. I guess that's not correct way anymore?

[AriParkkila]

Include headers added already in #7304