Improve RSA sing performance by 20-30% by:
- switching from floating-point to integer conditional moves;
- daisy-chaining sqr-sqr-sqr-sqr-sqr-mul sequences;
- using MONTMUL even during powers table setup;
(cherry picked from commit 4ddacd99)

(cherry picked from commit 3b848d34)

(cherry picked from commit 42b9a417)

(cherry picked from commit cd8d7335)

(cherry picked from commit c7f690c2)

(cherry picked from commit 32213d8d)

(cherry picked from commit b4275915)

(cherry picked from commit 1bc0b68d)

(cherry picked from commit cdb6c484)

Fix PSS signature printing: consistently use 0x prefix for hex values for
padding length and trailer fields.
(cherry picked from commit deb24ad53147f5a8dd63416224a5edd7bbc0e74a)

(cherry picked from commit 96940f4f2d0300c033379a87db0ff19e598c6264)

previous cbc128.c commit].

(cherry picked from commit b69437e1)

(cherry picked from commit 4df2280b)

(and pending AVX2 changes).
(cherry picked from commit 504bbcf3)

(cherry picked from commit 988d11b6)