Remove spi locking hack + increase max sd frequency

These two changes (mostly the former) dramatically increase
responsiveness when doing database updates; previously we were suffering
from some nasty priority inversion.

afaict the underlying need to acquire_spi seems to be fixed? i.e. spi
bus acquisition is working properly. fingers heavily heavily crossed.

src/drivers/display.cpp

@@ -296,6 +296,8 @@ void Display::SendTransaction(TransactionType type,
 void Display::OnLvglFlush(lv_disp_drv_t* disp_drv,
                           const lv_area_t* area,
                           lv_color_t* color_map) {
+  spi_device_acquire_bus(handle_, portMAX_DELAY);
+
   // First we need to specify the rectangle of the display we're writing into.
   uint16_t data[2] = {0, 0};
 
@@ -314,6 +316,8 @@ void Display::OnLvglFlush(lv_disp_drv_t* disp_drv,
   SendCommandWithData(displays::ST77XX_RAMWR,
                       reinterpret_cast<uint8_t*>(color_map), size * 2);
 
+  spi_device_release_bus(handle_);
+
   if (!first_flush_finished_ && lv_disp_flush_is_last(disp_drv)) {
     first_flush_finished_ = true;
     SetDisplayOn(display_on_);

src/drivers/include/drivers/spi.hpp

@@ -13,6 +13,6 @@ namespace drivers {
 
 esp_err_t init_spi(void);
 esp_err_t deinit_spi(void);
-std::lock_guard<std::mutex> acquire_spi(void);
+int acquire_spi(void);
 
 }  // namespace drivers

src/drivers/spi.cpp

@@ -56,8 +56,10 @@ esp_err_t deinit_spi(void) {
   return spi_bus_free(kSpiHost);
 }
 
-std::lock_guard<std::mutex> acquire_spi(void) {
-  return std::lock_guard<std::mutex>{sSpiMutex};
+int acquire_spi(void) {
+  // Cross fingers emoji: I *think* this is now resolved???
+  // return std::lock_guard<std::mutex>{sSpiMutex};
+  return 1;
 }
 
 }  // namespace drivers

src/drivers/storage.cpp

@@ -57,6 +57,7 @@ auto SdStorage::Create(IGpios& gpio) -> cpp::result<SdStorage*, Error> {
   }
 
   auto host = std::make_unique<sdmmc_host_t>(sdmmc_host_t SDSPI_HOST_DEFAULT());
+  host->max_freq_khz = SDMMC_FREQ_HIGHSPEED;
   auto card = std::make_unique<sdmmc_card_t>();
 
   host->slot = handle;