Linux 5.16 compat: asm/fpu/xcr.h is new location for xgetbv/xsetbv

Linux 5.16 moved these functions into this new header in commit
1b4fb8545f2b00f2844c4b7619d64d98440a477c. This change adds code to look
for the presence of this header, and include it so that the code using
xgetbv & xsetbv will compile again.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #12800