KVM: SVM: Name and check reserved fields with structs offset

Rename reserved fields on all structs in arch/x86/include/asm/svm.h
following their offset within the structs. Include compile time checks for
this in the same place where other BUILD_BUG_ON for the structs are.

This also solves that fields of struct sev_es_save_area are named by their
order of appearance, but right now they jump from reserved_5 to reserved_7.

Link: https://lkml.org/lkml/2022/10/22/376


Signed-off-by: Carlos Bilbao <carlos.bilbao@amd.com>
Message-Id: <20221024164448.203351-1-carlos.bilbao@amd.com>
[Use ASSERT_STRUCT_OFFSET + fix a couple wrong offsets. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>