ArmPlatform/ArmPlatformLib: Introduced ArmPlatformPeiBootAction()

ArmPlatform/ArmPlatformLib: Introduced ArmPlatformPeiBootAction()

This function allows platform to do any specific actions prior to
the start the PEI phase.
For instance, this function could be used by some platforms to initialize clocks that
are required at the early stage of the PEI phase.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Acked-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14347 6f19259b-4bc3-4df7-8a09-765794883524