Revert "arm64: gicv3: Insert barriers after SGI operations"

This reverts commit 4507cc73 ("arm64: gicv3: Insert barriers after SGI operation"),
since the SGI barriers workaround is only needed for early 8996
parts.

CRs-Fixed: 960849
Change-Id: Ib946bd2ccd865aeb467b5d8cdc365fcda3b61e0b
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>