mmc: core: new discard feature support at Samsung eMMC v4.41+.

Support discard feature if MID field in the CID register is 0x15, EXT.CSD[192]
(device version) is 5 and Bit 0 in the EXT.CSD[64] is 1. Also removed REQ_SECURE flag
check to avoid kernel hang.

This patch is released from samsung.