doc: announce hiding interrupt handle structure

doc: announce hiding interrupt handle structure

Moving struct rte_intr_handle as an internal structure to
avoid any ABI breakages in future. Since this structure defines
some static arrays and changing respective macros breaks the ABI.
Eg:
Currently RTE_MAX_RXTX_INTR_VEC_ID imposes a limit of maximum 512
MSI-X interrupts that can be defined for a PCI device, while PCI
specification allows maximum 2048 MSI-X interrupts that can be used.
If some PCI device requires more than 512 vectors, either change the
RTE_MAX_RXTX_INTR_VEC_ID limit or dynamically allocate based on
PCI device MSI-X size on probe time. Either way its an ABI breakage.

Discussion thread:
https://mails.dpdk.org/archives/dev/2021-March/202959.html

Signed-off-by: Harman Kalra <hkalra@marvell.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: Chenbo Xia <chenbo.xia@intel.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>