Optimize ef_write_block function: The function did single byte writing until a start of a page was detected. Only in that case a multi byte write was used. According to the manual page write is not limited to 256 byte. Multiple bytes may be written until the end of the page is reached => Changed implementation to always use multi byte writes which increases the performance of the write block function

Imported from Ac6/SystemWorkbench/plugins/fr.ac6.mcu.firmware_1.14.7.201711101414/resources/builtin/:
* File syscalls.c