tools/xen-hvmctx: drop bogus casts from dump_cpu()

tools/xen-hvmctx: drop bogus casts from dump_cpu()

Also avoid printing the MSR flags (they're always zero as of commit
2f1add6e1c "x86/vmx: Don't leak host syscall MSR state into HVM
guests"), and print FPU registers only when the respective flag
indicates the space holds valid data.

Adjust format specifiers a little at the same time, in particular to
avoid at least some leading zeros to be printed when the positions
can't ever be non-zero. This helps readability in my opinion.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>