x86/hvm: rearrange content of hvm.h

x86/hvm: rearrange content of hvm.h

Move enum and function declarations to first half of the file.

Static inline functions and macros, which reference HVM specific
fields directly are grouped together in second half of the file.

The movement is needed because in a later patch the second half is
going to be enclosed in CONFIG_HVM.

Pure code movement. No functional change.

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