prevent starting a 32-bit VM using a 64-bit OVMF BIOS

prevent starting a 32-bit VM using a 64-bit OVMF BIOS

Instead of starting a VM with a 32-bit CPU type and a 64-bit OVMF image,
throw an error before starting the VM telling the user that OVMF is not
supported on 32-bit CPU types.

To obtain a list of 32-bit CPU types, refer to the builtin_x86_defs in
target/i386/cpu.c of QEMU. Exclude any entries that have the long mode
feature (CPUID_EXT2_LM).

Signed-off-by: Filip Schauer <f.schauer@proxmox.com>