mtd: hyperbus: Fix build failure when only RPCIF_HYPERBUS is enabled

commit 5de15b61 ("mtd: hyperbus: add Renesas RPC-IF driver") leads
to build failure[1] with COMPILE_TEST and RPCIF_HYPERBUS enabled. This
is because driver needs functions RENESAS_RPCIF which is only buildable
for CONFIG_ARCH_RENESAS.

Fix this by dropping COMPILE_TEST from RPCIF_HYPERBUS Kconfig entry.
This ensures driver can be built only when RENESAS_RPCIF is also
selected.

[1]:
rpc-if.c:(.text+0x20): undefined reference to `rpcif_disable_rpm' ld:
drivers/mtd/hyperbus/rpc-if.o: in function `rpcif_hb_prepare_read':
rpc-if.c:(.text+0xd6): undefined reference to `rpcif_prepare' ld:
drivers/mtd/hyperbus/rpc-if.o: in function `rpcif_hb_read16':
[...]

Fixes: 5de15b61

 ("mtd: hyperbus: add Renesas RPC-IF driver") leads
Reported-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Richard Weinberger <richard@nod.at>