Match the generic_64bitonly_x86_64/BoardConfig.mk to generic_x86_64

aosp_64bitonly_x86_64 gets broken by the emulator
changes otherwise.

Bug: 274103438
Test: m
Change-Id: I31fed64619e26a1c690a6cf086c644757e45a878
Signed-off-by: Roman Kiryanov <rkir@google.com>