fix(sme): synchronize context before using it

We need to wait for the write to cptr_el2 to take effect to consider SME
enabled. Otherwise, the write to smcr_el2 may fault. Add an isb() to
synchronize this.

Change-Id: Ib1fb1803bad2d4fb9e89bc4861e2e611b9882b2e
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
1 file changed