at91: rename mem_init() to at91_mem_init()

The AT91-based platforms have a mem_init() function declared in
arch/arm/mach-at91/include/mach/at91_common.h and implemented in various
places. In preparation of the introduction of the lwIP networking library
which also has a global mem_init() function, rename the AT91 one to
at91_mem_init().

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Hari Prasath Gujulan Elango <hari.prasathge@microchip.com>
diff --git a/board/atmel/at91sam9x5ek/at91sam9x5ek.c b/board/atmel/at91sam9x5ek/at91sam9x5ek.c
index e5688c6..f52b9a9 100644
--- a/board/atmel/at91sam9x5ek/at91sam9x5ek.c
+++ b/board/atmel/at91sam9x5ek/at91sam9x5ek.c
@@ -181,7 +181,7 @@
 		      2 << ATMEL_MPDDRC_TPR2_TXARD_OFFSET);
 }
 
-void mem_init(void)
+void at91_mem_init(void)
 {
 	struct at91_pmc *pmc = (struct at91_pmc *)ATMEL_BASE_PMC;
 	struct at91_matrix *matrix = (struct at91_matrix *)ATMEL_BASE_MATRIX;