Revert most of the series for adding vexpress_aemv8r support

Per a request from Andre Przywara and agreed with by Peter Hoyes, the
vexpress aemv8r support wasn't quite ready to be merged, but the
discussion had moved off list.  We should keep the first patch in the
series for now, but revert the rest.  This reverts the following
commits:

e0bd6f31 doc: Add documentation for the Arm vexpress board configs
30e5a449 arm: Use armv8_switch_to_el1 env to switch to EL1
b53bbca6 vexpress64: Add BASER_FVP vexpress board variant
2f5b7b74 armv8: Add ARMv8 MPU configuration logic
37a757e2 armv8: Ensure EL1&0 VMSA is enabled

Signed-off-by: Tom Rini <trini@konsulko.com>