x86/cpufeatures: Add feature bit RDPRU on AMD

AMD Zen 2 introduces a new RDPRU instruction which is used to give
access to some processor registers that are typically only accessible
when the privilege level is zero.

ECX is used as the implicit register to specify which register to read.
RDPRU places the specified register’s value into EDX:EAX.

For example, the RDPRU instruction can be used to read MPERF and APERF
at CPL > 0.

Add the feature bit so it is visible in /proc/cpuinfo.

Details are available in the AMD64 Architecture Programmer’s Manual:
https://www.amd.com/system/files/TechDocs/24594.pdf

Signed-off-by: Babu Moger <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Aaron Lewis <[email protected]>
Cc: [email protected]
Cc: Fenghua Yu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: "Peter Zijlstra (Intel)" <[email protected]>
Cc: [email protected]
Cc: Thomas Gleixner <[email protected]>
Cc: Thomas Hellstrom <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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