On 64bit architectures TLSF_64BIT should be defined. Decide that
depending on the CONFIG_64BIT symbol. When 64bit support is enabled
all allocations will be aligned to 8 byte boundaries which is necessary
for architectures that do not support unaligned accesses or have
a performance penalty for unaligned accesses.
Also changes the undefined tlsf_decl to 'static'.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>