s390/zcrypt: Improve EP11 CPRB length and overflow checks

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

s390/zcrypt: Improve EP11 CPRB length and overflow checks

The xcrb_msg_to_type6_ep11cprb_msgx() function lacks proper input
validation, creating security vulnerabilities:
1. Missing minimum size validation: The ep11_cprb structure and
subsequent payload fields (pld_tag, pld_lenfmt) are copied from
userspace without verifying sufficient buffer length.
2. Arithmetic overflow in length calculations: CEIL4 alignment could
overflow, bypassing size checks and enabling buffer overflows.
3. The payload is asn1 encoded but the function just uses a simple c
struct overlay to access some fields of the payload.

Fix by using size_t for length calculations, adding U32_MAX boundary
checks after alignment, and validating minimum request size and
minimum reply size before copying from userspace. Do a very simple
asn1 parsing of the payload up to the function value field.