hyperv: Avoid -Wflex-array-member-not-at-end warning

hyperv: Avoid -Wflex-array-member-not-at-end warning

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the new __TRAILING_OVERLAP() helper to fix the following warning:

include/hyperv/hvgdk_mini.h:581:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM) and a
set of MEMBERS that would otherwise follow it.

This overlays the trailing MEMBER u64 gva_list[]; onto the FAM
struct hv_tlb_flush_ex::hv_vp_set.bank_contents[], while keeping
the FAM and the start of MEMBER aligned.

The static_assert() ensures this alignment remains, and it's
intentionally placed inmediately after the related structure --no
blank line in between.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Wei Liu <wei.liu@kernel.org>