arm32: Align arguments of sync_icache() syscall to cacheline size.

Otherwise, we may miss synchronization of the last cacheline.

Approved by: re (gjb)

(cherry picked from commit ec090f4a67654fa541e6d97fd5f74d3f66c1c0d0)
(cherry picked from commit 6930f97474e409808ca5e220c2b3a86805f786b8)