conf/multilib.conf: Add ovmf to NON_MULTILIB_RECIPES

conf/multilib.conf: Add ovmf to NON_MULTILIB_RECIPES

Fixed:
MACHINE = "qemux86-64"
require conf/multilib.conf
MULTILIBS = "multilib:lib32"
DEFAULTTUNE_virtclass-multilib-lib32 = "x86"

$ bitbake ovmf lib32-ovmf
[snip]
ERROR: ovmf-edk2-stable201905-r0 do_deploy_setscene: The recipe ovmf is trying to install files into a shared area when those files already exist.
 Those files and their manifest location are:
  /buildarea1/lyang1/rebase-work/test_cc/tmp-glibc/deploy/images/qemux86-64/OvmfPkKek1.key
    (matched in manifest-qemux86_64-lib32-ovmf.deploy)
[snip]

Add it NON_MULTILIB_RECIPES to fix the problem since it is a firmware, build
multilib for it doens't make much sense.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>