s390/zcrypt: Improve CCA CPRB length and overflow checks

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

s390/zcrypt: Improve CCA CPRB length and overflow checks

The xcrb_msg_to_type6cprb_msgx() function lacks proper input
validation, creating security vulnerabilities:
1. Integer overflow after CEIL4 alignment: Signed int variables could
overflow during 4-byte boundary alignment, causing undersized
buffer allocations or incorrect bounds checking.
2. Missing minimum size validation: The CPRBX structure is copied from
userspace without verifying sufficient buffer length. Undersized
buffers cause uninitialized memory access when reading structure
fields like cprbx.cprb_len and cprbx.domain.
3. Arithmetic overflow in sum calculations: Adding control block and
data block sizes could overflow, bypassing size checks and enabling
buffer overflows.

Fix by using size_t for length calculations, adding U32_MAX boundary
checks after alignment, validating minimum control block size before
copying from userspace, and detecting sum calculation overflows.