CVE-2026-23346: arm64: io: Extract user memory type in ioremap_prot()

In the Linux kernel, the following vulnerability has been resolved:

arm64: io: Extract user memory type in ioremapprot()

The only caller of ioremapprot() outside of the generic ioremap() implementation is genericaccessphys(), which passes a 'pgprott' value determined from the user mapping of the target 'pfn' being accessed by the kernel. On arm64, the 'pgprott' contains all of the non-address bits from the pte, including the permission controls, and so we end up returning a new user mapping from ioremapprot() which faults when accessed from the kernel on systems with PAN:

| Unable to handle kernel read from unreadable memory at virtual address ffff80008ea89000 | ... | Call trace: | memcpyfromio+0x80/0xf8 | genericaccessphys+0x20c/0x2b8 | accessremotevm+0x46c/0x5b8 | accessremotevm+0x18/0x30 | environread+0x238/0x3e8 | vfsread+0xe4/0x2b0 | ksysread+0xcc/0x178 | arm64sysread+0x4c/0x68

Extract only the memory type from the user 'pgprott' in ioremapprot() and assert that we're being passed a user mapping, to protect us against any changes in future that may require additional handling. To avoid falsely flagging users of ioremap(), provide our own ioremap() macro which simply wraps ioremapprot().