x86/sev: Map only the RMP table entries instead of the full RMP range

In preparation for support of a segmented RMP table, map only the RMP
table entries. The RMP bookkeeping area is only ever accessed when
first enabling SNP and does not need to remain mapped. To accomplish
this, split the initialization of the RMP bookkeeping area and the
initialization of the RMP entry area. The RMP bookkeeping area will be
mapped only while it is being initialized.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikunj A Dadhania <nikunj@amd.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Reviewed-by: Ashish Kalra <ashish.kalra@amd.com>
Link: https://lore.kernel.org/r/22f179998d319834f49c13a8c01187fbf0fd308d.1733172653.git.thomas.lendacky@amd.com