common/cnxk: update CPU directive in NPA assembly code

common/cnxk: update CPU directive in NPA assembly code

Use arch_extension instead of .cpu directive in NPA assembly code
snippets. Using .cpu directive with generic causes it to override
the micro architecture selected by march,mcpu.
For example if march=armv8.5-a+crypto+sve2 provided then the .cpu
directive overrides it to generic+crypto+sve2, use arch_extension
to get the expected result.

Signed-off-by: Ashwin Sekhar T K <asekhar@marvell.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>