SP ECC: ecc_point - add padding when 16 byte aligned

[SparkiDev]

Description

To make 16-byte aligned points, add padding to end.

Testing

./configure --disable-shared --enable-sp --enable-sp-asm --enable-fpecc
./configure --disable-shared --enable-sp --enable-sp-asm --enable-fpecc CFLAGS=-DSP_ALIGN_16

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[devin-ai-integration]

🛟 Devin Lifeguard found 1 likely issues in this PR

• struct-member-order snippet: Place the 15-byte pad before the 1-byte infinity field (… z[34]; byte pad[15]; byte infinity; …) so that members are ordered from larger to smaller and no larger field follows a smaller one.

@SparkiDev
please take a look at the above issues which Devin flagged. Devin will not fix these issues automatically.

[douzzer]

alas, seeing the same failure as we've seen all along:

[    2.346119] wolfssl: ecc_test_curve(): ecc_test_curve_size 66 failed!
[    2.346878] wolfssl: ecc_test(): keySize=66, Default
[    2.347464] wolfssl: wc_test_render_error_message(): ECC      test failed!
[    2.347464]  error L=33348