x86/sev: Shorten struct name snp_secrets_page_layout to snp_secrets_page

Ending a struct name with "layout" is a little redundant, so shorten the
snp_secrets_page_layout name to just snp_secrets_page.

No functional change.

  [ bp: Rename the local pointer to "secrets" too for more clarity. ]

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/bc8d58302c6ab66c3beeab50cce3ec2c6bd72d6c.1713974291.git.thomas.lendacky@amd.com