s390/uv: Rename find_secret() to uv_find_secret() and publish

Rename the internal UV function find_secret() to uv_find_secret()
and publish it as new UV API in-kernel function.

The pkey uv handler may be called in a do-not-allocate memory
situation where sleeping is allowed but allocating memory which
may cause IO operations is not. For example when an encrypted
swap file is used and the encryption is done via UV retrievable
secrets with protected keys.

The UV API function uv_get_secret_metadata() allocates memory
and then calls the find_secret() function. By exposing the
find_secret() function as a new UV API function uv_find_secret()
it is possible to retrieve UV secret meta data without any
memory allocations from the UV when the caller offers space
for one struct uv_secret_list.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Acked-by: Holger Dengler <dengler@linux.ibm.com>
Link: https://lore.kernel.org/r/20250424133619.16495-22-freude@linux.ibm.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>