firmware: scm: Remove arch check for dma_set_mask

Remove the preprocessor if statement for checking the arch of the
target since this will not affect targets with a 32bit address space. This
change allows the driver to be compiled and used for targets that do not
define CONFIG_ARM64.

Change-Id: I6fc11e86d6799099fdaeec46df6d7093c1ca117f
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Tushar Nimkar <tnimkar@codeaurora.org>
Signed-off-by: Siddharth Gupta <sidgup@codeaurora.org>