sysutils/edk2: Add qemu_x64 and qemu_i386 as new FLAVORs of edk2

Instead of having a separate sysutils/uefi-edk2-qemu port, add qemu_x64
and qemu_i386 as FLAVORs of sysutils/edk2 and delete sysutils/uefi-edk2-qemu.

Differential Revision: https://reviews.freebsd.org/D35408
Approved by: manu