digsig: replace call to long_log2() with ilog2()

Replace a call to renamed function long_log2() with ilog2() from
linux/log2.h, in digsig_init_caching().

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: replace use of write_tryseqlock() in digsig_cache_signature()

Replace use of removed function write_tryseqlock() with spin_trylock()
and write_seqcount_begin() in digsig_cache_signature().

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: replace manual spinlock definition with DEFINE_SPINLOCK()

Replace a manual spinlock definition using a removed macro constant
with DEFINE_SPINLOCK().

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: add old crypto header

This patch adds the old Scatterlist Cryptographic API so that the
module may build.

This patch should be reviewed at a later date and reimplemented more
elegantly, using the modern API.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: use sg_set_page() in digsig_sha1_update()

Use sg_set_page() instead of manual struct field assignment in
digsig_sha1_update().

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: replace asm/scatterlist.h inclusion

Replace inclusion of asm/scatterlist.h with linux/scatterlist.h in
dsi_sig_verify.h.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>