add UEFI load support for arm64

[jongwu]

Hello @bonzini @jiangliu

I find in the cloud-hypervisor that the linux_loader can be used for loading Ovmf Image for x86, as it can be in the same format of x86 kernel. But that is not the case for arm64 as Virtual Arm64 UEFI Image is not in format of PE. So should we add UEFI image load support for arm64 here?
I think that the implementation is just like linux_loader but removing the header check.

@justin-he @michael2012z @MrXinWang