xen/xsm: Compile error due to naming clash between XSM and EFI runtime

xen/xsm: Compile error due to naming clash between XSM and EFI runtime

The problem is that efi_runtime_call is the name of both a function in
xen/arch/x86/efi/runtime.c and a member of the xsm_operations struct
in xen/include/xsm/xsm.h. This causes the macro "#define
efi_runtime_call(x) efi_compat_runtime_call(x)" on line 15 of
xen/arch/x86/x86_64/platform_hypercall.c to cause the above compile
error.

Renaming the XSM struct member fixes the problem.

Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>
Acked-by: Jan Beulich <jbeulich@suse.com>