gstreamer1: add libatomic dependency for 32-bit arm targets

gstreamer1: add libatomic dependency for 32-bit arm targets

arm926ej-s (ARMv5) does not have native lock-free atomics and the
toolchain inserts calls to libatomic.so.1 for atomic operations.
The libgstreamer1 DEPENDS only listed armeb, powerpc, mips and mipsel
as needing libatomic, missing plain arm (little-endian 32-bit ARM).

Extend the condition to include arm so the package is properly
declared on all 32-bit ARM targets that require libatomic.

Signed-off-by: Alexandru Ardelean <redacted>