OvmfPkg/QemuKernelLoaderFsDxe: don't expose kernel command line

OvmfPkg/QemuKernelLoaderFsDxe: don't expose kernel command line

We have no need for exposing the kernel command line as a file,
so remove support for that. Since the remaining blobs (kernel
and initrd) are typically much larger than a page, switch to
the page based allocator for blobs at the same time.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2566
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>