ARM64: arch_timer: add support to configure and enable event stream

This patch adds support for configuring the event stream frequency
and enabling it.

It also adds the hwcaps as well as compat-specific definitions to
the user to detect this event stream feature.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
Git-commit: 46efe547aca8498d51b64460c02366ae4032ca32
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[imaund@codeaurora.org: resolve merge conflict]
Signed-off-by: Ian Maund <imaund@codeaurora.org>