[media] allow COMPILE_TEST for SAMSUNG_EXYNOS4_IS

That helps some static checks, so enable it. While there, it was
noticed that linux/sizes.h was missing:

drivers/media/platform/exynos4-is/mipi-csis.c: In function ‘s5pcsis_s_rx_buffer’:
drivers/media/platform/exynos4-is/mipi-csis.c:114:31: error: ‘SZ_4K’ undeclared (first use in this function)
 #define S5PCSIS_PKTDATA_SIZE  SZ_4K
                               ^

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>