ArmPkg/TimerDxe: add workaround for KVM timer interrupt handling

ArmPkg/TimerDxe: add workaround for KVM timer interrupt handling

KVM on ARM currently masks the timer interrupt on the timer side when
delivering an interrupt to the guest. This itself is a workaround for an
issue where the interrupt is reraised and trapped by the host as soon as
the guest is entered, resulting in the guest being starved.

Work around this by calling ArmGenericTimerEnable () after servicing each
interrupt. The virtual version of ArmGenericTimerCounterLib will then
make sure to unmask the interrupt again.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-By: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16144 6f19259b-4bc3-4df7-8a09-765794883524