packagegroup-core-standalone-sdk-target: Add libgcov-dev to on device SDK

packagegroup-core-standalone-sdk-target: Add libgcov-dev to on device SDK

When a user takes coverage in gcc of SDK, it becomes the link error in SDK
because there is not libgcov.

----
ld: cannot find -lgcov
collect2: error: ld returned 1 exit status
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(From OE-Core rev: 99b26dba6e4f5a64579f183883265498000e3104)

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>