Rework bootmethod initialization

We currently initialize the bootmethod late, in assembly code. This
requires us to maintain the el3/no_el3 distintion late into the boot
process, and means we cannot produce any helpful diagnostic when booted
at an unexpected exception level.

Rework things so that we initialize the bootmethod early, with a warning
when things are wrong. The el3/no_el3 distinction is now irrelevant to
the bootmethod code, and can be removed in subsequent patches.

When a boot-wrapper configured for PSCI is entered at EL2, a warning is
looged to the serial console as:

| Boot-wrapper v0.2
| Entered at EL2
| Memory layout:
| [0000000080000000..0000000080001f90] => boot-wrapper
| [000000008000fff8..0000000080010000] => mbox
| [0000000080200000..00000000822af200] => kernel
| [0000000088000000..0000000088002857] => dtb
|
| WARNING: PSCI could not be initialized. Boot may fail

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
12 files changed