arm64: defconfig: Trim genericarmv8 defconfig

Remove unwanted configs for VM.

MemTotal increased by approx. 4MB and MemFree
increased by approx. 6MB.

Change-Id: I27781fe9f2d7edf2e0464d6e9d1d5259e07cf525
Signed-off-by: Keerthi Gowda Balehalli Satyanarayana <kbalehal@codeaurora.org>