KVM: arm64: vgic-its: Add debugfs interface to expose ITS tables

KVM: arm64: vgic-its: Add debugfs interface to expose ITS tables

This commit introduces a debugfs interface to display the contents of the
VGIC Interrupt Translation Service (ITS) tables.

The ITS tables map Device/Event IDs to Interrupt IDs and target processors.
Exposing this information through debugfs allows for easier inspection and
debugging of the interrupt routing configuration.

The debugfs interface presents the ITS table data in a tabular format:

    Device ID: 0x0, Event ID Range: [0 - 31]
    EVENT_ID    INTID  HWINTID   TARGET   COL_ID HW
    -----------------------------------------------
           0     8192        0        0        0  0
           1     8193        0        0        0  0
           2     8194        0        2        2  0

    Device ID: 0x18, Event ID Range: [0 - 3]
    EVENT_ID    INTID  HWINTID   TARGET   COL_ID HW
    -----------------------------------------------
           0     8225        0        0        0  0
           1     8226        0        1        1  0
           2     8227        0        3        3  0

    Device ID: 0x10, Event ID Range: [0 - 7]
    EVENT_ID    INTID  HWINTID   TARGET   COL_ID HW
    -----------------------------------------------
           0     8229        0        3        3  1
           1     8230        0        0        0  1
           2     8231        0        1        1  1
           3     8232        0        2        2  1
           4     8233        0        3        3  1

The output is generated using the seq_file interface, allowing for efficient
handling of potentially large ITS tables.

This interface is read-only and does not allow modification of the ITS
tables. It is intended for debugging and informational purposes only.

Signed-off-by: Jing Zhang <jingzhangos@google.com>
Link: https://lore.kernel.org/r/20250220224247.2017205-1-jingzhangos@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>