xen: cache cr0 value to avoid trap'n'emulate for read_cr0
xen: cache cr0 value to avoid trap'n'emulate for read_cr0

stts() is implemented in terms of read_cr0/write_cr0 to update the
state of the TS bit.  This happens during context switch, and so
is fairly performance critical.  Rather than falling back to
a trap-and-emulate native read_cr0, implement our own by caching
the last-written value from write_cr0 (the TS bit is the only one
we really care about).

Impact: optimise Xen context switches
Signed-off-by: Jeremy Fitzhardinge <35cfe9f678a9e9bbdcf2f6e68cd105ce06d149b1@citrix.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs