ACPICA: Add new MADT GICC flags fields [code first?]

Add the new flag field to the MADT's GICC structure.

'Online Capable' indicates a disabled CPU can be enabled later.

Signed-off-by: James Morse <james.morse@arm.com>
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This patch probable needs to go via the upstream acpica project,
but is included here so the feature can be testd.