boot1.efi: use malloc family from libsa

The zfs reader development did reach to the point where linking boot1,
we will get errors about duplicate symbols Malloc, Free, Calloc.

We can just use libsa version, just as loader.efi does. The only concern is,
libsa zalloc is using fixed size heap region, I did pick 64MB as other
stage instances are using, but this size is likely not optimal. In any case,
with limited memory setups, we should boot loader.efi directly.

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