icecc.bbclass: Fix different signatures with ICECC_DISABLED

:Release Notes:
When enabled set_icecc_env has dependency on ARMPKGSFX_FPU variable.

:Detailed Notes:
List of dependencies for variable set_icecc_env changed from ...
changed items: set(['ARMPKGSFX_FPU'])
Dependency on variable ARMPKGSFX_FPU was added

:Testing Performed:
Only build tested and verified with sstate-diff-machines.sh that the
signatures are identical again with and without ICECC_DISABLED set.

:QA Notes:
No change to image.

:Build Notes:
Invalidates all sstate signatures.

:Issues Addressed:
[ES-725] ICECC environment is created regardless of the value of
         ICECC_DISABLED

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I89b225497242b6f0f391da84883dd7546c95352a
Reviewed-on: https://g2g.palm.com/5547
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: DCO Verification
Build: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Build Verification